Final Report Summary - CAMEL-MCG (Development of highly efficient and environmentally friendly grinding technology through a minimum coolant approach)
Executive summary:
Grinding plays an important role in the development of tools and in the production of steam engines, internal combustion engines, bearings, transmissions, and ultimately, jet engines, astronomical instruments, and micro-electronic devices. This process requires very high input of energy per unit volume of work-material removed. Virtually all the energy is converted to heat, which can cause high work-piece temperature and related thermal damage such as grinding burn, phase transformation, tensile residual stresses, surface cracks, reduced fatigue strength, thermal distortion and inaccuracies. Normally, a large amount of cutting fluids is applied to improve the grinding performance. Most of the cutting fluids used are formulated from mineral oils, which are one of the most unsustainable elements of grinding processes. In addition, the chronic inhalation of oil-based mist has been shown to be responsible for serious health risks. As the environmental regulations become firmer, the cost of disposal or recycling also continues rising. As a consequence, there is a requirement to develop environmentally aware and cost-effective near dry or minimum quantity lubrication (MQL) grinding processes.
MQL grinding has several key technical barriers, including the high wheel wear, limited material removal rate, work-piece thermal damage, generation of fumes, and accumulation of chips both in the grinding wheel and the machine enclosure. The minimal coolant grinding (MCG) technique would provide to all cutting grains the required cooling fluid, in a minimal quantity but without losing effectiveness. The technique is based on the use of two nozzles, not necessarily placed very close to the grinding wheel. The first nozzle will launch an oil spray which will enter through the wheel pores. Then, the second nozzle will launch a gas which will freeze the oil or transforms it in a viscose substance in order to facilitate the adherence to the grains. In the cutting area, the frozen or adhered oil is liquefied progressively by the heat generated. In that manner, the amount of oil in the grinding zone will be higher than MQL techniques increasing the efficiency of the process.
In the first part of this project, besides the development of the MCG prototypes for different grinding operations in the research and technological development (RTD) institute facilities, simulation software able to predict the optimal MCG grinding process parameters were developed. During the trials, the forces, surface roughness, grinding wheel wear, temperatures and residual stresses were assessed for MQL, MCG and flood cooling with conventional 5 % soluble oil. The experiments showed the best performance in terms of surface roughness, power consumption and wheel life was achieved by MCG. In the case of residual stresses compressive values were obtained in the MCG and MQL ground parts but with lower values than conventional flood cooling.
Therefore, the best surface quality was obtained with conventional techniques. In the second part of this project an intensive work was done in the industrialisation of the MCG. An exhausting system composed by an industrial vacuum cleaner connected to a special nozzle able to clean both the grinding wheel and the machine closure was developed. Once the technology was optimised it was established in the end users facilities showing that MCG has a high potential to diminish production costs and improve competitiveness by dropping resource consumption and generating less waste.
Project context and objectives:
Grinding is the common collective name for machining processes which utilise hard abrasive particles as the cutting medium. Nowadays, grinding is a major manufacturing process which accounts for 20 - 25 % of the total expenditures on machining operation in industrialised countries. Society, as we know it, would be quite impossible without grinding. Almost everything that we use has either been machined by grinding at some stage of its production, or has been processed by machines which owe their precision to abrasive operations. Grinding is traditionally regarded as a final machining process in the production of extreme hardness of brittleness components requiring smooth surfaces and fine tolerances.
The grinding process requires extremely high energy expenditure per unit volume of material removed. These energy levels are much higher than those in machining operations. This difference can be attributed to factors such as the presence of a wear flat and chips produced with a high negative rake angle. Nearly, all of this energy is converted to heat which is concentrated within the contact zone. In fact, the production rates are often limited by grinding temperatures and their deleterious influence on workpiece. Therefore, to improve the performance the vast majority of the grinding operations are performed with the aid of a grinding fluid.
Grinding fluids are generally considered to have two main roles: lubrication and cooling. Grinding fluids can also help to keep the wheel surface clean and provide corrosion protection for newly machined surfaces. Lubrication by grinding fluids reduces the friction and wear associated with the grinding process, thereby allowing for more efficient operation with less consumption of the abrasive. Bulk cooling of the work piece by applied fluid decreases the inaccuracies associated with thermal expansion and distortion of the workpiece.
On the other hand, the cost of grinding fluids is approximately 15 % of the lifecycle operational cost of a grinding process. It includes the costs associated with procurement, filtration, separation and disposal. Already the costs for disposal of coolant are higher than the initial cost of the coolant, and they are still rising. Even stricter regulations are under consideration for coolant usage, disposal and worker protection. As a result of all of this, coolant in wet grinding operations is a crucial economic issue.
The MQL technique is gaining acceptance as a cost-saving and environmentally friendly option in place of some wet machining processes like turning and drilling. This technique is based on the avoidance of the emergence of heat by reducing the friction between tool and work piece by providing the working zone with minimum amounts of lubricant. MQL permits dramatic cuts in coolant costs: 10 - 40 ml / h in MQL vs. 30 - 200 l / min in flood cooling, while protecting workers and the environment. It also delivers improved tool life and surface finish - even though tool life is often the reason why wet machining is applied. MQL can deliver better life for two reasons: (1) the optimum concentration of lubrication can be specified for a given operation; and (2) silicon particle contamination suspended in the cutting fluid is eliminated.
MQL technique has had a very low application in grinding processes, since it is necessary to traverse the grinding wheel pores and these constitute a real labyrinth in a random way. This specific feature of the grinding process makes traditional MQL systems used in turning and drilling not feasible for grinding, and nowadays there are not industrial applications in this field. Throwing a small spray of lubricant over the wheel (as in MQL techniques) does not reach all the contact area and it is impossible to have proper lubrication.
The attempt of the MCG system which will be developed in this project solves this problem, taking up the wheel pores with frozen lubricant. The oil is thrown by a nozzle and after a cryogenic gas from a second nozzle freezes this oil. This lubricant is fixed in the pores, close to the grains and the conglomerate, and liquefies when it arrives to the contact zone, cooling both the wheel and the workpiece. Lubricant freezing has not only the function of cooling, but also of fixing efficiently the lubricant to the contact area. In the figure, we can observe how the fluid enters into the pores. The cryogenic gas freezes the oil which is dragged until the cutting zone where it is liquefied again. The main objective of the project is to prove that MCG is viable and sustainable technology in comparison to flood cooling in conventional grinding. For that an industrial case study will be evaluated in terms of the total production cost per part, covering all sustainability measures.
The MCG technique is conceptually simple, but the success of its application depends on several factors that must be independently analysed, although all of them are at the end jointly implemented on the industrial prototype:
(a) nozzles, both are different; one is for gas and the other for oil spray;
(b) gas flow, speed and temperature;
(c) grinding wheel features: the bonding system of the grains must be adequate;
(d) lubricant: coolant speed, characteristics at high and low temperatures, freezing point, and facility to be adhered with the abrasive grains and the bonding;
(e) exhausting system to eliminate the waste generated during grinding in near dry conditions.
Project results:
Along the CAMEL-MCG project life, the research performed by the partners has both theoretical and experimental activities, supported by industrial evaluations at the beneficiaries' shop floor and production systems.
For the first period of the project (month 0 to month 9), performed activity had a big component of theoretical analysis of the heat transmission on the grinding zone, as it is critical to characterise appropriately the technology. The wrong selection of setting parameters can cause thermal damage of the workpiece surface and significant rise of manufacturing costs. For this reason, fundamental understanding of the grinding process, especially the physical phenomena in the contact zone, is a key factor for a productive machining with grinding wheels.
The finite difference model developed by Magdeburg University represents a flexible solution of different combinations of boundary conditions for the analysis of the thermal phenomena in the workpiece during a grinding process. For the solution of the heat equation, the finite difference method (FDM) has been used. In direct comparison of FDM with the analytical model by Carslaw and Jaeger, the FDM is more flexible and allows solving of the problem on finite domain. The principle of the model is very similar to the analytical model by Carslaw and Jager, however the dimensions of the workpiece are finite and the boundary conditions can be easily implemented.
The developed model is based on the replacement of the partial derivatives in the heat equation 1 by finite differences.
From the experimental data has been found that the heat transfer coefficient is about 25 000 Wm-2 K-1, for the MQL grinding process and 40 000 Wm-2 K-1 for the wet grinding.
The algorithm for solving the heat equation by the FDM has been programming in JAVA language and can run on any java virtual machine regardless of computer architecture.
The second main objective for this first period has been the setting up of the different mechanical elements that will be fundamental on the optimum performance of the MCG process.
Prior to analyse the performance of the technology another important role must be solved: how to remove the metallic chips and the dust generated by the wheels wear. The solution developed by Ideko and Bremen for cylindrical and surface grinding respectively has the same principle that consists in connect a special nozzle to an industrial vacuum cleaner equipped with filter inserts for extracting chips, oil mist and carbon dioxide (CO2) out of the working room.
To evaluate the cleaning effect of the exhausting system, grinding tests with and without vacuum cleaning have been performed and the wheel load has been assessed. It can be taken from the pictures that after grinding without using the exhausting system a high amount of chips can be detected on the wheel surface.
Once the complete prototypes with the MGC technology have been developed for both cylindrical and surface grinding, they were ready to assess the maximum ability of the process. The first task developed in that field was the selection of the best shape for the MQL and the CO2 supply nozzles. The shape of the coolant jet and the spray behaviour for the different nozzles has been investigated by high speed videos. Furthermore, the CO2 flow rate dependent on the gas pressure was examined as well as the temperature for certain distances after the nozzle orifice.
For the determination of jet shape and spray behaviour the air supply and the air pressure at the MQL supply system were varied. An investigation by STEIDLE regarding the influence of the air supply and air pressure adjusted by a regulating valve has shown that with increasing air supply and pressure the flow rate of air also increases. An almost steady state of the flow rate is reached with 1.25 turns of the regulation valve for air supply independent from air pressure.
At low air supply of the MQL system a constant oil supply over the cross section of the oil spray cannot be achieved. Drop sizes of up to 1 mm for the needle jet nozzle and 0.8 mm for the flat spray nozzle have been observed at what the drop velocity was quite low. Thus, for both nozzles a low air supply has been considered to lead to a non-uniform moistening of the grinding wheel during the process. A jet width of 15 mm in a distance of 30 mm after the nozzle orifice can be determined for the needle jet nozzle, for the flat spray nozzle a width of 45 mm of the jet has been measured.
In the following, the results for a high air supply with varying air pressure will be discussed. The high-speed videos have shown that by increasing air pressure a uniform aerosol generation and a smaller drop size can be noticed. Furthermore, by increasing air pressure the jet speed is also increasing, but a determination of the jet speed according to the air pressure was not possible due to the small drop size.
In contrast to the findings regarding the needle jet nozzle, the high-speed videos of the flat spray nozzle have shown that the jet speed is nearly independent from the air pressure. In addition to that, a nearly uniform aerosol generation, with few bigger drops occurring, can be determined with an air pressure of 2 bar. In the case of an air pressure of 3 bar, a higher amount of bigger drops has been detected within the oil spray.
In the case of MQL oil supply nozzles the jet needle nozzle has been chosen for the following grinding tests in work package 3. This nozzle enables a long distance between the nozzle orifice and the impact of the oil on the grinding wheel, especially in the case of surface grinding. In this regard, the flat spray nozzle generates the loss of a high amount of overspray due to the spray width of 45 mm in a distance of 30 mm after the orifice. With regard to environmental aspects, the flat spray nozzle has the advantage of decreased air consumption during the process due to the fact that an adequate and uniform aerosol generation can be achieved by adjusting an air pressure of 3 bar. This would lead to a reduction of up to 18% regarding the air consumption. However, the flat spray nozzle is more suitable for outer-diameter grinding processes due to a shorter distance between the grinding wheel and the MQL oil supply nozzle.
Comparable to the investigation of the MQL oil supply nozzles, different nozzles for CO2 supply have been assessed using high-speed videos. Two nozzles have been analysed the GAM 1190.
As can be seen in the following figure the nozzle Lechler 2507 is characterised by a strong jet expansion in a distance of up to 30 mm. Considering a grinding wheel width of 20 mm and a distance between the grinding wheel and the CO2 supply nozzle of more than 20 mm during the surface grinding tests, the nozzle Lechler 2507 is rather applicable against the nozzle GAM 1190 despite a high amount of overspray.
In the next section a summary of the work done by the UPV to find the optimal MCG grinding parameters for outer diameter cylindrical parts is presented. Characterisation of performance of a given grinding configuration involves studying aspects such as wheel wear and specific grinding energy.
The diameter of the specimen was 90mm. In order to find the limits of the technology tests roughing grinding test were performed with differents specific material removal rates Q'w of 3 and 5 mm3 / smm.
Using these parameters the influence of the following variables has been analysed:
- The nature of the MQL oil provide by OEMETA: FA1 and ET1.
- MQL flow: fl1= 3 ml / min; fl2= 8 ml / min; fl3= 15 ml / min.
- CO2 consumption: fl1= 1 Kg / min; fl2= 0.6 Kg / min; fl3= 0.4 Kg / min; fl4= 0.2 Kg / min.
In order to analyse the influence of the formulation of two oils provided by OEMETA: FA1 (fatty alcohol) and ET (ester oil) the same previous analysed has been done. Fom the grinding ratio comparison it is shown that OEMETA ET-1 produces an impressive improvement not only with respect to conventional cooling, but also with respect to OEMETA FA-1.
Another important variable to depict is the flow of the CO2 for that similar results have been done varying the flow rate from 1 to only 0.2 Kg /min. The best results has been obtained with a flow rate of 0.6 Kg / min.
Finally, the drastic reduction of coolant has the risk of an excessive increase of temperatures which could cause thermal damage. In order to see if the work pieces have suffered from burning, it has measured residual stresses on specimen surfaces using X-Ray diffractometry.
It can be seen that in the case of the parts ground using conventional cooling the main stress s2 is clearly compressive, whilst s1 is near zero. In the case of the parts ground using the MCG technology, s2 is always compressive but of a lower value than in conventional grinding. Although s1 is positive (tensile), a clear trend can be observed that correlates the nature of this main residual stress with the flow of CO2. When increasing the gas flow the value of the tensile stress is reduced. In other words, the deleterious effect of grinding temperatures decreases when gas flow is increased. That means the process is not valid for roughing operations.
After this analysis the optimal MCG conditions are:
- Oil type: OEMETA ET1.
- MQL flow: fl2= 8 ml / min.
- CO2 consumption: fl2= 0.6 Kg / min.
- Only valid for fine finishing operations with Q'w lower than 3 mm 3 / smm.
Similar methodology was followed by UoB to define the optimal setting parameters of the MCG for surface grinding. In the surface operation similar performance in terms of surface finish and power consumption of both coolant supply methods has been achieved.
The final technical step of the project has been the industrial validation done in the Jasil facilities. The OD part was ground in the cylindrical grinder of Jasil in Portugal whereas the connecting rod was ground in the facilities of Bremen University.
The first step was the installation of the MCG equipment: MQL, CO2 injection system, exhausting nozzle to clean both the wheel and the machine and the industrial vacuum cleaner in the grinder located in Jasil.
A friable Aluminum Oxide grit (2A) from DRAGAO with a special induced open structure to retain the highest amount of oil was designed for the MCG grinding. The grit size (60) and the hardness of the wheel (M) were selected in function to the roughness tolerances and stock removal rate specifications. Finally, a vitrified bond was used with the aim of supporting both the high level of the porosity and high temperature stability needed for this process.
Finally, in order to analyse the surface integrity of the ground surfaces a measurement of the residual stresses has been carried out using the X-ray diffractometer technique. Three work pieces from the overall batch have been analysed: the first, the tenth and the latest. Besides two measurements have been done per part: points A and B. Point B is located 180 degrees away from point A.
The results show that the surface integrity of both technologies are correct with better compressive stresses for the conventional cooling. After that we can conclude that MCG grinding for this kind of parts is technically viable.
Now the results for the connecting rod are presented. To evaluate the limits of the MCG technology four test series have been designed and performed with the aim to reduce the cycle time for the grinding operation. The test series were performed under usage of the MCG system and conventional coolant supply as well. The grinding strategy in terms of depth of cut, cutting sequence and the overlap rate in dressing were varied while the tangential feed speed vft = 25 m / min and the cutting speed vc =30 m / s have been kept constant. Furthermore, two different grinding wheels with a grit size of 46 and 80 mesh have been used. During the grinding tests, the energy consumption of the machine tool has been measured. For the assessment of the surface integrity of the ground parts, surface roughness has been evaluated as well as thermal damage of the workpiece by nital etching.
To assess and to compare the energy consumption of the grinding tests with the MCG system and conventional coolant supply the consumed energy per part has been calculated.
It can be assumed that the energy consumption per part decreases with decreasing cycle time. Also, the influence of the dressing process on the used energy can be seen. A higher overlap in dressing leads to higher energy consumption per part due to the extended duration of the dressing process. The comparison between the CAMEL system and the conventional coolant supply shows clearly that the CAMEL system generally causes higher energy consumption. This can be explained by the high demand for energy of the supporting equipment (exhausting and CO2 system).
In general, the surface roughness values show that the MCG approach leads to less surface roughness values. Furthermore, the reduction of the cycle time by increased depth of cut causes higher roughness values for both coolant supply approaches. This effect can be explained by a change of the wheel topography due to increasing stress of the grinding wheel at higher depths of cut are resulting in higher wear and roughness of the grinding wheel surface.
The residual stress depth profiles show a change from compressive residual stresses of the initial state of about 300 MPa to almost tensile residual stresses at the surface. This indicates a thermal influence on the ground workpiece during grinding with the MCG system and supports the results after nital etching. Furthermore, the influence of the grit size is obvious: Due to the higher friction caused by the less grain size of 80 mesh the increasing thermal effect leads to higher tensile residual stresses at the surface of the ground parts.
In the following lines a summary of the industrial application results is presented:
Regarding the energy consumption the usage of the MCG system during surface grinding and cylindrical grinding leads generally to a higher consumption (approximately 20 up to 30 %). This effect is resulting from the supporting equipment (exhauster, CO2 system) of the MCG approach.
The surface and subsurface properties of the ground work pieces after surface grinding with the MCG system are characterised by lower roughness values.
For the con rod grinding both coolant supply strategies (MCG and conventional coolant supply) slight thermal damage of the ground surfaces has been detected. If the low grade of thermal damage affects the mechanical properties and the operational behaviour of the parts could not be verified. However in the case of cylindrical grinding operation due to the kinematics of the process and the fine finishing grinding conditions no thermal damage has been detected.
To convince of the potential of the new technology a production cost analysis and Life cycle assessment have to be done. Costs in precision cylindrical grinding are compared for different technologies and grinding conditions. The analysis is for repeated batch production with the methodology and conditions showed in the Deliverable 4.1. Account is taken of machine cost, abrasive cost and fluid lubricant cooling cost. Cost comparisons were based on extensive trials to assess re-dress life against workpiece quality requirements. Easy-to-grind hardened steel was ground at conventional speeds.
Despite the cost of the machine rate and the coolant cost is higher for the MCG the lower consume of the grinding wheels and higher production rates makes the total production cost saving of 16 %, for the crankshaft grinding. In order to evaluate the environmental effect of a process, the impact resulting from each stage of its life cycle has to be considered. A quantitative assessment of the environmental impact is evaluated with an additional health semi quantitative assessment associated with MCG process in comparison to conventional flooding. The results from the comparison of material production impacts broken down by component suggest that surfactants dominate the emissions for three of the six impact categories: energy use, acidification, and solid waste. Flood cooling MCG Based on LCA, it can be observed that for MCG, in comparison to conventional flooding, a switch to a lower emulsion concentration can yield reductions in global-warming potential (GWP), acidification, and solid waste, while these reductions are associated with an increase in energy use. In short, in cryogenic machining there is a compromise as regards higher energy use and a cleaner machining process. As we know that the production of CO2 requires electrical energy consumption, we can talk about such being a sustainable machining process only when using a renewable energy source (wind, solar, hydro, etc.). When the coolant fluid is at the end of its useful life, it has to be disposed of. In MCG, the fluids immediately evaporate after being delivered to the cutting zone, leaving no residuals, and there is no need for recycling. On the other hand, in the conventional the coolant fluid has to be removed from the workpiece, chips, etc. after the grinding process, and then collected and recycled. All this represents additional processes, costs, and environmental burdens. The usual procedure for oil based CLF disposal consists of drying the emulsion and its subsequent combustion. In contrast to oils, emulsions do not have high energetic values; therefore the combustion process must take into account the high potential for additional environmental burdens. Although combustion does recover some energy from the waste coolant fluid, it additionally highly impacts GWP and acidification.
Including recycling requirements, the conclusion that MCG has drastically lower environmental emissions in comparison to oil-based coolant fluids, in most impact categories, is robust with regard to different end of life cycle options, e.g. combustion, etc.
With regard to worker health and safety chronic inhalation of oil-based mists has been shown to be responsible for serious health risks. Such emulsion mists can harbour bacteria, and contain surfactants, biocides, chlorinated fatty, chelating agents and defoamers, all of which are harmful to health. This is notable since surfactants and biocides have been found to impair lung functioning. None of these materials are present in evaporated CO2. More importantly, it has been proven that machining mist can be eliminated in MCG grinding. In addition to mists, oil-based coolants can cause dermatitis and other skin irritations. They also tend to result in the accumulation of an oily sludge on and around the production plant over time. Spills can also be a rather regular workplace hazard, but can be eliminated by using MCG cooling. On the other hand, in MCG grinding less likely but more serious safety issues are required, related to the extremely low temperature of the pipes delivering the CO2, which can cause physical burns in the event of contact.
Therefore can be conclude that the challenges in production with regard to the economy and the environment taking into account the overall life cycle of the Coolant fluid have been discussed in this deliverable. In that sense, MCG is presented as viable and sustainable grinding technology in comparison to flood cooling. For both technologies a comparative LCA was conducted. The LCA demonstrated that moving from oil-based CLFs to MCG grinding is a move towards more sustainable grinding process. Changing from oil-based to MCG can reduce the solid waste, water usage, global warming potential, acidification, and in an increased energy use for coolant fluid production. While oil-based emulsions are highly developed after decades of research and development in this field, MCG grinding has only just recently been studied in depth in this work. With knowledge of their relative capabilities, it is believed that sustainable alternative machining performance improvements are likely possible.
Potential impact:
The potential economic impact of the project is high and the consortium quantifies it according to the following benefits:
- 40 % reduction in the generation of waste and energy consumption.
- 20% of reduction of cost associated of each workpiece, due to respective reductions in energetic cost, lubricant and coolant cost, cutting fluid recycling cost, required floor space and wheel consumption.
- Promising application opportunities in fine finishing grinding in many industrial sectors as automotive parts, cutting tool production, aerospace components, etc.
Apart from the general benefits taken from the results of the project, partners will profit from specific products resulting from the project.
MQL system for MCG processes
The MQL systems require an adaptation for MCG processes. The main difference between grinding and defined edge machining, is the big contact length for grinding. Oil droplets from MQL systems have to cover a bigger surface, length and wide. More open oil jets and flow rates of oil and pressurised air are required.
Devices in MQL system have to be revised, nozzles, pneumatic pumps and other components have to be modified.
Grinding wheels
New grinding wheels adapted for MCG machining need improved capacity to carry frozen oil to grinding point, wheel porosity, conglomerate material and grit size have to modified in order to achieve the best oil carrying conditions.
Abrasive grits, as well as conglomerate grits, are modified to meet the new thermal and dynamic conditions of cutting.
MCG optimised process
The implementation of optimised processes for MCG will decrease costs in grinding operations. Energy costs, grinding waste disposal costs, liquids and sludge, are drastically reduced.
Another improvement for the company will be the reduction on floor occupation, big conventional cooling liquid tanks are no longer necessary. As land cost is high, reductions of occupied land are important.
Lubricant oil
Oil for MCG demands the qualities common to all MQL oils, as well as new specific properties for MCG, particularly improvement of capacity to be easily frozen without an excessive amount of cooling energy.
New lubrication oil formulations have to be prepared for the MCG process.
MCG optimised process
The implementation of optimised processes for MCG will reduce costs in grinding operations. Energy costs, grinding waste disposal costs, liquids and sludge, are drastically decreased.
Another improvement for the company will be the reduction on floor occupation, big conventional cooling liquid tanks are no longer necessary. As land cost is high, reductions of occupied land are important.
Finally a new, efficient, and ecological process will be a clear commercial advantage for the company.
Machine equipment
The main result for KONDIA will be the design and development of a grinding machine tool specially equipped for grinding parts using the MCG technique, eliminating conventional coolant equipment.
This machine will have a great impact mainly in automotive industries, as well as all companies using grinding processes. Cost of coolant is drastically diminished, grinding sludge and filters disposal costs are eliminated, grinding machine footprint is decreased as coolant tank is no necessary, power consumption is reduced.
The machine performance is ameliorated, machining cost are reduced and ecological impact is improved.
Components
The implementation of the complete system will also mean the development of specific devices for the grinding machines: chip extraction system, connections to external aspiration pump, grinding wheel headstock adaptation to MQL and Cryogenic gas implementation, working table and work piece headstock modifications.
These components could also be installed on grinding machines retrofitted for MCG machining. Machine adaptation for MCG will open a new market for Kondia.
Dissemination activities
Several dissemination activities have been performed by the CAME-MCG consortium. These actions include preparing materials for dissemination, attending relevant fairs and congresses related to grinding activities, publishing papers in scientific journals and developing, and continuously updating, a website for the project.
Material for dissemination
Different items for dissemination were prepared. Among them a poster and leaflets depicting the main activities and results obtained in the project. This material, poster and leaflets, was used for several dissemination activities carried out by partners attending exhibition fairs related to grinding activities. Finally a movie depicting MCG technology was created, showing the main advantages of the process. This movie was uploaded to the project website for public access.
Industrial Fair and exhibitions
CAMEL- MCG project was disseminated through the most important exhibitions related to machine tool and for grinding in Europe and outside Europe.
Events on which the CAMEL project was disseminated is as follows:
- GRINDTEC exhibition (Augsburg, March 2012): DRAGAO presented the project to visitors, showed a poster and delivered CAMEL-MCG leaflets. UoB had a presentation of the CAMEL-MCG poster.
- METAV exhibition (Düsseldorf, March 2012): OEMETA and STEIDLE showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- AMB exhibition (Stuttgart, September 2012): OEMETA and STEIDLE showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- AMB China (Nanjing, October 2012): OEMETA showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- Beneficiaries attended the fair, presenting on their booths, Camel-MCG Project development, objectives and results were presented in different ways.
(1) A poster describing the topics of the project, all beneficiaries and their role in the project was exhibited. The CAMEL poster is shown up on the left.
(2) People from project beneficiaries attended the fair answering questions set up by interested visitors on MCG technology.
(3) Leaflets depicting MCG principles and advantages, project summary and activities were exhibited.
Scientific dissemination
Scientific dissemination was carried out by RTD partners in two ways, presentation of CAMEL-MCG technology in scientific congresses and publishing of technical papers on indexed journals.
- A presentation on MCG technology was given at the most influent scientific congresses related to grinding and machining processes.
- CIRP General Assembly (Hong-Kong, August 2012): UoB and OVGU shared the presentation of a technical paper.
- ISAAT XV (International Symposium on Advanced Abrasive Technologies, Singapore, September 2012): UPV carried out a presentation.
Two scientific papers related to MCG technology were prepared and accepted for publication in scientific journals.
Strategies for optimal use of fluids in grinding R.Alberdi J.A.Sanchez I.Pombo N.Ortega B.Izquierdo S.Plaza D.Barrenetxea. International Journal of Machine Tools & Manufacture, 2011, Vol 51 issue 6 pag.491-499.
Reduction of oil and gas consumption in grinding technology using high pour-point lubricants E.Garcia I.Pombo J.A. Sanchez, N.Ortega B.Izquierdo S.Plaza J.I. Marquinez, C.Heinzel D.Mourek Journal of Cleaner Production, 2013; Vol.3 issue 3 Pag.300-307.
Project Website
From the beginning of the project a website was created. Along the development of the project, the site has been, and will be, regularly updated until the end of the project. The site is divided in two areas, a private area for project partners, which is used for circulating all information corresponding to the project, and to store important documents (deliverables, description of work, consortium agreement, etc.). The other area is public and it is used as dissemination tool for the project.
List of websites: http://www.camel-project.eu
Grinding plays an important role in the development of tools and in the production of steam engines, internal combustion engines, bearings, transmissions, and ultimately, jet engines, astronomical instruments, and micro-electronic devices. This process requires very high input of energy per unit volume of work-material removed. Virtually all the energy is converted to heat, which can cause high work-piece temperature and related thermal damage such as grinding burn, phase transformation, tensile residual stresses, surface cracks, reduced fatigue strength, thermal distortion and inaccuracies. Normally, a large amount of cutting fluids is applied to improve the grinding performance. Most of the cutting fluids used are formulated from mineral oils, which are one of the most unsustainable elements of grinding processes. In addition, the chronic inhalation of oil-based mist has been shown to be responsible for serious health risks. As the environmental regulations become firmer, the cost of disposal or recycling also continues rising. As a consequence, there is a requirement to develop environmentally aware and cost-effective near dry or minimum quantity lubrication (MQL) grinding processes.
MQL grinding has several key technical barriers, including the high wheel wear, limited material removal rate, work-piece thermal damage, generation of fumes, and accumulation of chips both in the grinding wheel and the machine enclosure. The minimal coolant grinding (MCG) technique would provide to all cutting grains the required cooling fluid, in a minimal quantity but without losing effectiveness. The technique is based on the use of two nozzles, not necessarily placed very close to the grinding wheel. The first nozzle will launch an oil spray which will enter through the wheel pores. Then, the second nozzle will launch a gas which will freeze the oil or transforms it in a viscose substance in order to facilitate the adherence to the grains. In the cutting area, the frozen or adhered oil is liquefied progressively by the heat generated. In that manner, the amount of oil in the grinding zone will be higher than MQL techniques increasing the efficiency of the process.
In the first part of this project, besides the development of the MCG prototypes for different grinding operations in the research and technological development (RTD) institute facilities, simulation software able to predict the optimal MCG grinding process parameters were developed. During the trials, the forces, surface roughness, grinding wheel wear, temperatures and residual stresses were assessed for MQL, MCG and flood cooling with conventional 5 % soluble oil. The experiments showed the best performance in terms of surface roughness, power consumption and wheel life was achieved by MCG. In the case of residual stresses compressive values were obtained in the MCG and MQL ground parts but with lower values than conventional flood cooling.
Therefore, the best surface quality was obtained with conventional techniques. In the second part of this project an intensive work was done in the industrialisation of the MCG. An exhausting system composed by an industrial vacuum cleaner connected to a special nozzle able to clean both the grinding wheel and the machine closure was developed. Once the technology was optimised it was established in the end users facilities showing that MCG has a high potential to diminish production costs and improve competitiveness by dropping resource consumption and generating less waste.
Project context and objectives:
Grinding is the common collective name for machining processes which utilise hard abrasive particles as the cutting medium. Nowadays, grinding is a major manufacturing process which accounts for 20 - 25 % of the total expenditures on machining operation in industrialised countries. Society, as we know it, would be quite impossible without grinding. Almost everything that we use has either been machined by grinding at some stage of its production, or has been processed by machines which owe their precision to abrasive operations. Grinding is traditionally regarded as a final machining process in the production of extreme hardness of brittleness components requiring smooth surfaces and fine tolerances.
The grinding process requires extremely high energy expenditure per unit volume of material removed. These energy levels are much higher than those in machining operations. This difference can be attributed to factors such as the presence of a wear flat and chips produced with a high negative rake angle. Nearly, all of this energy is converted to heat which is concentrated within the contact zone. In fact, the production rates are often limited by grinding temperatures and their deleterious influence on workpiece. Therefore, to improve the performance the vast majority of the grinding operations are performed with the aid of a grinding fluid.
Grinding fluids are generally considered to have two main roles: lubrication and cooling. Grinding fluids can also help to keep the wheel surface clean and provide corrosion protection for newly machined surfaces. Lubrication by grinding fluids reduces the friction and wear associated with the grinding process, thereby allowing for more efficient operation with less consumption of the abrasive. Bulk cooling of the work piece by applied fluid decreases the inaccuracies associated with thermal expansion and distortion of the workpiece.
On the other hand, the cost of grinding fluids is approximately 15 % of the lifecycle operational cost of a grinding process. It includes the costs associated with procurement, filtration, separation and disposal. Already the costs for disposal of coolant are higher than the initial cost of the coolant, and they are still rising. Even stricter regulations are under consideration for coolant usage, disposal and worker protection. As a result of all of this, coolant in wet grinding operations is a crucial economic issue.
The MQL technique is gaining acceptance as a cost-saving and environmentally friendly option in place of some wet machining processes like turning and drilling. This technique is based on the avoidance of the emergence of heat by reducing the friction between tool and work piece by providing the working zone with minimum amounts of lubricant. MQL permits dramatic cuts in coolant costs: 10 - 40 ml / h in MQL vs. 30 - 200 l / min in flood cooling, while protecting workers and the environment. It also delivers improved tool life and surface finish - even though tool life is often the reason why wet machining is applied. MQL can deliver better life for two reasons: (1) the optimum concentration of lubrication can be specified for a given operation; and (2) silicon particle contamination suspended in the cutting fluid is eliminated.
MQL technique has had a very low application in grinding processes, since it is necessary to traverse the grinding wheel pores and these constitute a real labyrinth in a random way. This specific feature of the grinding process makes traditional MQL systems used in turning and drilling not feasible for grinding, and nowadays there are not industrial applications in this field. Throwing a small spray of lubricant over the wheel (as in MQL techniques) does not reach all the contact area and it is impossible to have proper lubrication.
The attempt of the MCG system which will be developed in this project solves this problem, taking up the wheel pores with frozen lubricant. The oil is thrown by a nozzle and after a cryogenic gas from a second nozzle freezes this oil. This lubricant is fixed in the pores, close to the grains and the conglomerate, and liquefies when it arrives to the contact zone, cooling both the wheel and the workpiece. Lubricant freezing has not only the function of cooling, but also of fixing efficiently the lubricant to the contact area. In the figure, we can observe how the fluid enters into the pores. The cryogenic gas freezes the oil which is dragged until the cutting zone where it is liquefied again. The main objective of the project is to prove that MCG is viable and sustainable technology in comparison to flood cooling in conventional grinding. For that an industrial case study will be evaluated in terms of the total production cost per part, covering all sustainability measures.
The MCG technique is conceptually simple, but the success of its application depends on several factors that must be independently analysed, although all of them are at the end jointly implemented on the industrial prototype:
(a) nozzles, both are different; one is for gas and the other for oil spray;
(b) gas flow, speed and temperature;
(c) grinding wheel features: the bonding system of the grains must be adequate;
(d) lubricant: coolant speed, characteristics at high and low temperatures, freezing point, and facility to be adhered with the abrasive grains and the bonding;
(e) exhausting system to eliminate the waste generated during grinding in near dry conditions.
Project results:
Along the CAMEL-MCG project life, the research performed by the partners has both theoretical and experimental activities, supported by industrial evaluations at the beneficiaries' shop floor and production systems.
For the first period of the project (month 0 to month 9), performed activity had a big component of theoretical analysis of the heat transmission on the grinding zone, as it is critical to characterise appropriately the technology. The wrong selection of setting parameters can cause thermal damage of the workpiece surface and significant rise of manufacturing costs. For this reason, fundamental understanding of the grinding process, especially the physical phenomena in the contact zone, is a key factor for a productive machining with grinding wheels.
The finite difference model developed by Magdeburg University represents a flexible solution of different combinations of boundary conditions for the analysis of the thermal phenomena in the workpiece during a grinding process. For the solution of the heat equation, the finite difference method (FDM) has been used. In direct comparison of FDM with the analytical model by Carslaw and Jaeger, the FDM is more flexible and allows solving of the problem on finite domain. The principle of the model is very similar to the analytical model by Carslaw and Jager, however the dimensions of the workpiece are finite and the boundary conditions can be easily implemented.
The developed model is based on the replacement of the partial derivatives in the heat equation 1 by finite differences.
From the experimental data has been found that the heat transfer coefficient is about 25 000 Wm-2 K-1, for the MQL grinding process and 40 000 Wm-2 K-1 for the wet grinding.
The algorithm for solving the heat equation by the FDM has been programming in JAVA language and can run on any java virtual machine regardless of computer architecture.
The second main objective for this first period has been the setting up of the different mechanical elements that will be fundamental on the optimum performance of the MCG process.
Prior to analyse the performance of the technology another important role must be solved: how to remove the metallic chips and the dust generated by the wheels wear. The solution developed by Ideko and Bremen for cylindrical and surface grinding respectively has the same principle that consists in connect a special nozzle to an industrial vacuum cleaner equipped with filter inserts for extracting chips, oil mist and carbon dioxide (CO2) out of the working room.
To evaluate the cleaning effect of the exhausting system, grinding tests with and without vacuum cleaning have been performed and the wheel load has been assessed. It can be taken from the pictures that after grinding without using the exhausting system a high amount of chips can be detected on the wheel surface.
Once the complete prototypes with the MGC technology have been developed for both cylindrical and surface grinding, they were ready to assess the maximum ability of the process. The first task developed in that field was the selection of the best shape for the MQL and the CO2 supply nozzles. The shape of the coolant jet and the spray behaviour for the different nozzles has been investigated by high speed videos. Furthermore, the CO2 flow rate dependent on the gas pressure was examined as well as the temperature for certain distances after the nozzle orifice.
For the determination of jet shape and spray behaviour the air supply and the air pressure at the MQL supply system were varied. An investigation by STEIDLE regarding the influence of the air supply and air pressure adjusted by a regulating valve has shown that with increasing air supply and pressure the flow rate of air also increases. An almost steady state of the flow rate is reached with 1.25 turns of the regulation valve for air supply independent from air pressure.
At low air supply of the MQL system a constant oil supply over the cross section of the oil spray cannot be achieved. Drop sizes of up to 1 mm for the needle jet nozzle and 0.8 mm for the flat spray nozzle have been observed at what the drop velocity was quite low. Thus, for both nozzles a low air supply has been considered to lead to a non-uniform moistening of the grinding wheel during the process. A jet width of 15 mm in a distance of 30 mm after the nozzle orifice can be determined for the needle jet nozzle, for the flat spray nozzle a width of 45 mm of the jet has been measured.
In the following, the results for a high air supply with varying air pressure will be discussed. The high-speed videos have shown that by increasing air pressure a uniform aerosol generation and a smaller drop size can be noticed. Furthermore, by increasing air pressure the jet speed is also increasing, but a determination of the jet speed according to the air pressure was not possible due to the small drop size.
In contrast to the findings regarding the needle jet nozzle, the high-speed videos of the flat spray nozzle have shown that the jet speed is nearly independent from the air pressure. In addition to that, a nearly uniform aerosol generation, with few bigger drops occurring, can be determined with an air pressure of 2 bar. In the case of an air pressure of 3 bar, a higher amount of bigger drops has been detected within the oil spray.
In the case of MQL oil supply nozzles the jet needle nozzle has been chosen for the following grinding tests in work package 3. This nozzle enables a long distance between the nozzle orifice and the impact of the oil on the grinding wheel, especially in the case of surface grinding. In this regard, the flat spray nozzle generates the loss of a high amount of overspray due to the spray width of 45 mm in a distance of 30 mm after the orifice. With regard to environmental aspects, the flat spray nozzle has the advantage of decreased air consumption during the process due to the fact that an adequate and uniform aerosol generation can be achieved by adjusting an air pressure of 3 bar. This would lead to a reduction of up to 18% regarding the air consumption. However, the flat spray nozzle is more suitable for outer-diameter grinding processes due to a shorter distance between the grinding wheel and the MQL oil supply nozzle.
Comparable to the investigation of the MQL oil supply nozzles, different nozzles for CO2 supply have been assessed using high-speed videos. Two nozzles have been analysed the GAM 1190.
As can be seen in the following figure the nozzle Lechler 2507 is characterised by a strong jet expansion in a distance of up to 30 mm. Considering a grinding wheel width of 20 mm and a distance between the grinding wheel and the CO2 supply nozzle of more than 20 mm during the surface grinding tests, the nozzle Lechler 2507 is rather applicable against the nozzle GAM 1190 despite a high amount of overspray.
In the next section a summary of the work done by the UPV to find the optimal MCG grinding parameters for outer diameter cylindrical parts is presented. Characterisation of performance of a given grinding configuration involves studying aspects such as wheel wear and specific grinding energy.
The diameter of the specimen was 90mm. In order to find the limits of the technology tests roughing grinding test were performed with differents specific material removal rates Q'w of 3 and 5 mm3 / smm.
Using these parameters the influence of the following variables has been analysed:
- The nature of the MQL oil provide by OEMETA: FA1 and ET1.
- MQL flow: fl1= 3 ml / min; fl2= 8 ml / min; fl3= 15 ml / min.
- CO2 consumption: fl1= 1 Kg / min; fl2= 0.6 Kg / min; fl3= 0.4 Kg / min; fl4= 0.2 Kg / min.
In order to analyse the influence of the formulation of two oils provided by OEMETA: FA1 (fatty alcohol) and ET (ester oil) the same previous analysed has been done. Fom the grinding ratio comparison it is shown that OEMETA ET-1 produces an impressive improvement not only with respect to conventional cooling, but also with respect to OEMETA FA-1.
Another important variable to depict is the flow of the CO2 for that similar results have been done varying the flow rate from 1 to only 0.2 Kg /min. The best results has been obtained with a flow rate of 0.6 Kg / min.
Finally, the drastic reduction of coolant has the risk of an excessive increase of temperatures which could cause thermal damage. In order to see if the work pieces have suffered from burning, it has measured residual stresses on specimen surfaces using X-Ray diffractometry.
It can be seen that in the case of the parts ground using conventional cooling the main stress s2 is clearly compressive, whilst s1 is near zero. In the case of the parts ground using the MCG technology, s2 is always compressive but of a lower value than in conventional grinding. Although s1 is positive (tensile), a clear trend can be observed that correlates the nature of this main residual stress with the flow of CO2. When increasing the gas flow the value of the tensile stress is reduced. In other words, the deleterious effect of grinding temperatures decreases when gas flow is increased. That means the process is not valid for roughing operations.
After this analysis the optimal MCG conditions are:
- Oil type: OEMETA ET1.
- MQL flow: fl2= 8 ml / min.
- CO2 consumption: fl2= 0.6 Kg / min.
- Only valid for fine finishing operations with Q'w lower than 3 mm 3 / smm.
Similar methodology was followed by UoB to define the optimal setting parameters of the MCG for surface grinding. In the surface operation similar performance in terms of surface finish and power consumption of both coolant supply methods has been achieved.
The final technical step of the project has been the industrial validation done in the Jasil facilities. The OD part was ground in the cylindrical grinder of Jasil in Portugal whereas the connecting rod was ground in the facilities of Bremen University.
The first step was the installation of the MCG equipment: MQL, CO2 injection system, exhausting nozzle to clean both the wheel and the machine and the industrial vacuum cleaner in the grinder located in Jasil.
A friable Aluminum Oxide grit (2A) from DRAGAO with a special induced open structure to retain the highest amount of oil was designed for the MCG grinding. The grit size (60) and the hardness of the wheel (M) were selected in function to the roughness tolerances and stock removal rate specifications. Finally, a vitrified bond was used with the aim of supporting both the high level of the porosity and high temperature stability needed for this process.
Finally, in order to analyse the surface integrity of the ground surfaces a measurement of the residual stresses has been carried out using the X-ray diffractometer technique. Three work pieces from the overall batch have been analysed: the first, the tenth and the latest. Besides two measurements have been done per part: points A and B. Point B is located 180 degrees away from point A.
The results show that the surface integrity of both technologies are correct with better compressive stresses for the conventional cooling. After that we can conclude that MCG grinding for this kind of parts is technically viable.
Now the results for the connecting rod are presented. To evaluate the limits of the MCG technology four test series have been designed and performed with the aim to reduce the cycle time for the grinding operation. The test series were performed under usage of the MCG system and conventional coolant supply as well. The grinding strategy in terms of depth of cut, cutting sequence and the overlap rate in dressing were varied while the tangential feed speed vft = 25 m / min and the cutting speed vc =30 m / s have been kept constant. Furthermore, two different grinding wheels with a grit size of 46 and 80 mesh have been used. During the grinding tests, the energy consumption of the machine tool has been measured. For the assessment of the surface integrity of the ground parts, surface roughness has been evaluated as well as thermal damage of the workpiece by nital etching.
To assess and to compare the energy consumption of the grinding tests with the MCG system and conventional coolant supply the consumed energy per part has been calculated.
It can be assumed that the energy consumption per part decreases with decreasing cycle time. Also, the influence of the dressing process on the used energy can be seen. A higher overlap in dressing leads to higher energy consumption per part due to the extended duration of the dressing process. The comparison between the CAMEL system and the conventional coolant supply shows clearly that the CAMEL system generally causes higher energy consumption. This can be explained by the high demand for energy of the supporting equipment (exhausting and CO2 system).
In general, the surface roughness values show that the MCG approach leads to less surface roughness values. Furthermore, the reduction of the cycle time by increased depth of cut causes higher roughness values for both coolant supply approaches. This effect can be explained by a change of the wheel topography due to increasing stress of the grinding wheel at higher depths of cut are resulting in higher wear and roughness of the grinding wheel surface.
The residual stress depth profiles show a change from compressive residual stresses of the initial state of about 300 MPa to almost tensile residual stresses at the surface. This indicates a thermal influence on the ground workpiece during grinding with the MCG system and supports the results after nital etching. Furthermore, the influence of the grit size is obvious: Due to the higher friction caused by the less grain size of 80 mesh the increasing thermal effect leads to higher tensile residual stresses at the surface of the ground parts.
In the following lines a summary of the industrial application results is presented:
Regarding the energy consumption the usage of the MCG system during surface grinding and cylindrical grinding leads generally to a higher consumption (approximately 20 up to 30 %). This effect is resulting from the supporting equipment (exhauster, CO2 system) of the MCG approach.
The surface and subsurface properties of the ground work pieces after surface grinding with the MCG system are characterised by lower roughness values.
For the con rod grinding both coolant supply strategies (MCG and conventional coolant supply) slight thermal damage of the ground surfaces has been detected. If the low grade of thermal damage affects the mechanical properties and the operational behaviour of the parts could not be verified. However in the case of cylindrical grinding operation due to the kinematics of the process and the fine finishing grinding conditions no thermal damage has been detected.
To convince of the potential of the new technology a production cost analysis and Life cycle assessment have to be done. Costs in precision cylindrical grinding are compared for different technologies and grinding conditions. The analysis is for repeated batch production with the methodology and conditions showed in the Deliverable 4.1. Account is taken of machine cost, abrasive cost and fluid lubricant cooling cost. Cost comparisons were based on extensive trials to assess re-dress life against workpiece quality requirements. Easy-to-grind hardened steel was ground at conventional speeds.
Despite the cost of the machine rate and the coolant cost is higher for the MCG the lower consume of the grinding wheels and higher production rates makes the total production cost saving of 16 %, for the crankshaft grinding. In order to evaluate the environmental effect of a process, the impact resulting from each stage of its life cycle has to be considered. A quantitative assessment of the environmental impact is evaluated with an additional health semi quantitative assessment associated with MCG process in comparison to conventional flooding. The results from the comparison of material production impacts broken down by component suggest that surfactants dominate the emissions for three of the six impact categories: energy use, acidification, and solid waste. Flood cooling MCG Based on LCA, it can be observed that for MCG, in comparison to conventional flooding, a switch to a lower emulsion concentration can yield reductions in global-warming potential (GWP), acidification, and solid waste, while these reductions are associated with an increase in energy use. In short, in cryogenic machining there is a compromise as regards higher energy use and a cleaner machining process. As we know that the production of CO2 requires electrical energy consumption, we can talk about such being a sustainable machining process only when using a renewable energy source (wind, solar, hydro, etc.). When the coolant fluid is at the end of its useful life, it has to be disposed of. In MCG, the fluids immediately evaporate after being delivered to the cutting zone, leaving no residuals, and there is no need for recycling. On the other hand, in the conventional the coolant fluid has to be removed from the workpiece, chips, etc. after the grinding process, and then collected and recycled. All this represents additional processes, costs, and environmental burdens. The usual procedure for oil based CLF disposal consists of drying the emulsion and its subsequent combustion. In contrast to oils, emulsions do not have high energetic values; therefore the combustion process must take into account the high potential for additional environmental burdens. Although combustion does recover some energy from the waste coolant fluid, it additionally highly impacts GWP and acidification.
Including recycling requirements, the conclusion that MCG has drastically lower environmental emissions in comparison to oil-based coolant fluids, in most impact categories, is robust with regard to different end of life cycle options, e.g. combustion, etc.
With regard to worker health and safety chronic inhalation of oil-based mists has been shown to be responsible for serious health risks. Such emulsion mists can harbour bacteria, and contain surfactants, biocides, chlorinated fatty, chelating agents and defoamers, all of which are harmful to health. This is notable since surfactants and biocides have been found to impair lung functioning. None of these materials are present in evaporated CO2. More importantly, it has been proven that machining mist can be eliminated in MCG grinding. In addition to mists, oil-based coolants can cause dermatitis and other skin irritations. They also tend to result in the accumulation of an oily sludge on and around the production plant over time. Spills can also be a rather regular workplace hazard, but can be eliminated by using MCG cooling. On the other hand, in MCG grinding less likely but more serious safety issues are required, related to the extremely low temperature of the pipes delivering the CO2, which can cause physical burns in the event of contact.
Therefore can be conclude that the challenges in production with regard to the economy and the environment taking into account the overall life cycle of the Coolant fluid have been discussed in this deliverable. In that sense, MCG is presented as viable and sustainable grinding technology in comparison to flood cooling. For both technologies a comparative LCA was conducted. The LCA demonstrated that moving from oil-based CLFs to MCG grinding is a move towards more sustainable grinding process. Changing from oil-based to MCG can reduce the solid waste, water usage, global warming potential, acidification, and in an increased energy use for coolant fluid production. While oil-based emulsions are highly developed after decades of research and development in this field, MCG grinding has only just recently been studied in depth in this work. With knowledge of their relative capabilities, it is believed that sustainable alternative machining performance improvements are likely possible.
Potential impact:
The potential economic impact of the project is high and the consortium quantifies it according to the following benefits:
- 40 % reduction in the generation of waste and energy consumption.
- 20% of reduction of cost associated of each workpiece, due to respective reductions in energetic cost, lubricant and coolant cost, cutting fluid recycling cost, required floor space and wheel consumption.
- Promising application opportunities in fine finishing grinding in many industrial sectors as automotive parts, cutting tool production, aerospace components, etc.
Apart from the general benefits taken from the results of the project, partners will profit from specific products resulting from the project.
MQL system for MCG processes
The MQL systems require an adaptation for MCG processes. The main difference between grinding and defined edge machining, is the big contact length for grinding. Oil droplets from MQL systems have to cover a bigger surface, length and wide. More open oil jets and flow rates of oil and pressurised air are required.
Devices in MQL system have to be revised, nozzles, pneumatic pumps and other components have to be modified.
Grinding wheels
New grinding wheels adapted for MCG machining need improved capacity to carry frozen oil to grinding point, wheel porosity, conglomerate material and grit size have to modified in order to achieve the best oil carrying conditions.
Abrasive grits, as well as conglomerate grits, are modified to meet the new thermal and dynamic conditions of cutting.
MCG optimised process
The implementation of optimised processes for MCG will decrease costs in grinding operations. Energy costs, grinding waste disposal costs, liquids and sludge, are drastically reduced.
Another improvement for the company will be the reduction on floor occupation, big conventional cooling liquid tanks are no longer necessary. As land cost is high, reductions of occupied land are important.
Lubricant oil
Oil for MCG demands the qualities common to all MQL oils, as well as new specific properties for MCG, particularly improvement of capacity to be easily frozen without an excessive amount of cooling energy.
New lubrication oil formulations have to be prepared for the MCG process.
MCG optimised process
The implementation of optimised processes for MCG will reduce costs in grinding operations. Energy costs, grinding waste disposal costs, liquids and sludge, are drastically decreased.
Another improvement for the company will be the reduction on floor occupation, big conventional cooling liquid tanks are no longer necessary. As land cost is high, reductions of occupied land are important.
Finally a new, efficient, and ecological process will be a clear commercial advantage for the company.
Machine equipment
The main result for KONDIA will be the design and development of a grinding machine tool specially equipped for grinding parts using the MCG technique, eliminating conventional coolant equipment.
This machine will have a great impact mainly in automotive industries, as well as all companies using grinding processes. Cost of coolant is drastically diminished, grinding sludge and filters disposal costs are eliminated, grinding machine footprint is decreased as coolant tank is no necessary, power consumption is reduced.
The machine performance is ameliorated, machining cost are reduced and ecological impact is improved.
Components
The implementation of the complete system will also mean the development of specific devices for the grinding machines: chip extraction system, connections to external aspiration pump, grinding wheel headstock adaptation to MQL and Cryogenic gas implementation, working table and work piece headstock modifications.
These components could also be installed on grinding machines retrofitted for MCG machining. Machine adaptation for MCG will open a new market for Kondia.
Dissemination activities
Several dissemination activities have been performed by the CAME-MCG consortium. These actions include preparing materials for dissemination, attending relevant fairs and congresses related to grinding activities, publishing papers in scientific journals and developing, and continuously updating, a website for the project.
Material for dissemination
Different items for dissemination were prepared. Among them a poster and leaflets depicting the main activities and results obtained in the project. This material, poster and leaflets, was used for several dissemination activities carried out by partners attending exhibition fairs related to grinding activities. Finally a movie depicting MCG technology was created, showing the main advantages of the process. This movie was uploaded to the project website for public access.
Industrial Fair and exhibitions
CAMEL- MCG project was disseminated through the most important exhibitions related to machine tool and for grinding in Europe and outside Europe.
Events on which the CAMEL project was disseminated is as follows:
- GRINDTEC exhibition (Augsburg, March 2012): DRAGAO presented the project to visitors, showed a poster and delivered CAMEL-MCG leaflets. UoB had a presentation of the CAMEL-MCG poster.
- METAV exhibition (Düsseldorf, March 2012): OEMETA and STEIDLE showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- AMB exhibition (Stuttgart, September 2012): OEMETA and STEIDLE showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- AMB China (Nanjing, October 2012): OEMETA showed CAMEL-MCG poster, delivered leaflets, and discussed the project idea with (potential) customers.
- Beneficiaries attended the fair, presenting on their booths, Camel-MCG Project development, objectives and results were presented in different ways.
(1) A poster describing the topics of the project, all beneficiaries and their role in the project was exhibited. The CAMEL poster is shown up on the left.
(2) People from project beneficiaries attended the fair answering questions set up by interested visitors on MCG technology.
(3) Leaflets depicting MCG principles and advantages, project summary and activities were exhibited.
Scientific dissemination
Scientific dissemination was carried out by RTD partners in two ways, presentation of CAMEL-MCG technology in scientific congresses and publishing of technical papers on indexed journals.
- A presentation on MCG technology was given at the most influent scientific congresses related to grinding and machining processes.
- CIRP General Assembly (Hong-Kong, August 2012): UoB and OVGU shared the presentation of a technical paper.
- ISAAT XV (International Symposium on Advanced Abrasive Technologies, Singapore, September 2012): UPV carried out a presentation.
Two scientific papers related to MCG technology were prepared and accepted for publication in scientific journals.
Strategies for optimal use of fluids in grinding R.Alberdi J.A.Sanchez I.Pombo N.Ortega B.Izquierdo S.Plaza D.Barrenetxea. International Journal of Machine Tools & Manufacture, 2011, Vol 51 issue 6 pag.491-499.
Reduction of oil and gas consumption in grinding technology using high pour-point lubricants E.Garcia I.Pombo J.A. Sanchez, N.Ortega B.Izquierdo S.Plaza J.I. Marquinez, C.Heinzel D.Mourek Journal of Cleaner Production, 2013; Vol.3 issue 3 Pag.300-307.
Project Website
From the beginning of the project a website was created. Along the development of the project, the site has been, and will be, regularly updated until the end of the project. The site is divided in two areas, a private area for project partners, which is used for circulating all information corresponding to the project, and to store important documents (deliverables, description of work, consortium agreement, etc.). The other area is public and it is used as dissemination tool for the project.
List of websites: http://www.camel-project.eu
