PROJECT
HOLISTIC MODEL FOR THE DESIGN OF HSC PROCESSES
Abbildung 1: Profactor Produktionsforschungs GmbH
This project aimed to develop a systematic approach to the design and optimization of HSC processes in metal cutting. In addition to classic factors such as machining time, quality, and cost of the production process, investigations focused on occupational safety and environmental protection. Optimization of the process was realized in close cooperation with PIESSLINGER, a metal working company, and used a concrete aluminum component. Large numbers of this component have already successfully been produced for quite some time using HSC technology and minimum cooling lubrication.
The most important expectations at Piesslinger company referred to an improvement of working conditions with a view to indoor air quality and climate, noise and ergonomics, the increase in value of residue material such as aluminum chips, savings in cooling lubricant consumption in line with resource efficiency as well as an improved productivity and product quality.
The project consisted of the following steps:
- Experts’ workshop ascertaining the actual state of affairs and definition of objectives
- Development of a model of the process
- Planning and implementation of milling tests in the Profactor laboratory
- Planning and implementation of aerosol measurements in the laboratory
- Survey among employees by means of a questionnaire
- Workshop for employees: Presentation of test results and definition of a reference workplace
- Implementation of the planned measures
- Workshop for the evaluation of the experience from practice and identification of further need for action
Abbildung 2: Profactor Produktionsforschungs GmbH
RESULTS FROM THE MILLING TESTS
For the purpose of technological optimization, researchers performed milling tests in the laboratory using a reference work piece (a decorative aluminum part for coffee machines) and used varying key parameters for each test series. A total of 31 parameter combinations have been analyzed in the tests.
The milling tests identified, for each scenario, a favorable combination of tool coating and cooling lubricant system (MCL with optimized oil application and MCL using emulsion, respectively), which can reduce lubricant consumption.
Abbildung 3: Profactor Produktionsforschungs GmbH
Conventional machining of a component usually consumes approx. 1 liter of lubricant (oil) per work shift. This corresponds to a lubricant consumption of 6.6 ml/min. A change in the following parameters and an appropriate combination of parameters, respectively can reduce lubricant consumption by up to 75%:
- Tool coating
- Correct adjustment of spray nozzles
- Increased feed rates (from f=4000 to f=5000)
- Type of cooling lubricant
Especially the use of emulsion-based minimum cooling lubricants (6% oil, 94% water) can reduce lubricant consumption considerably. Also, tests using this system resulted in an improved surface finish. Recycling of the residue materials generated in the process (aluminum chips) strongly depends on the degree of soiling. Therefore, reducing the quantity of cooling lubricants has a positive effect on the quality of the aluminum chips. A shift from oil-based minimum lubrication to emulsion-based cooling lubricants further reduces impurities because most of the water evaporates during or after the milling process.
As the work piece and the material are virtually dry after machining with minimum lubrication, the cooling lubricant used in the process must have been discharged into the ambient air in the form of aerosol and vapor. The researchers measured the emissions discharged into the ambient air in the laboratory using a cascade impactor and ascertained the correlation between aerosol formation and the type of cooling lubricant method and the quantity of lubricant applied. Both systems (oil andemulsion) clearly showed a clear correlation between the amount of cooling lubricant used and aerosol concentration in the drawing-off air of the machine tool.
As minimum cooling lubricant systems use compressed air for atomization, misting levels tend to be higher than in conventional flood systems. However, this effect can be compensated by a consistent minimization of cooling lubricant consumption. In addition, an improved nozzle design for a more targeted application of the lubricant will probably solve this problem.
Abbildung 4: Profactor Produktionsforschungs GmbH
The milling tests used increased feed rates and reduced the quantity of cooling lubricant. It has been shown that increased feed rates permit a substantial reduction of lubricant. An impairment of quality occurred only when lubricant was reduced to 0.7 ml/min. Using emulsion reduces the proportion of oil to only 0.01 ml/min.
IMPLEMENTATION
A sustainable optimization of industrial processes requires a holistic view of the system as a whole as well as the integration of employees’ know-how and experience. The project involved all relevant actors in the planning and design of processes and work places. Employees participated in discussing the laboratory results and identified advantages and disadvantages of the two systems tested in the laboratory (minimum lubrication with optimized oil delivery and minimum lubrication using an emulsion).
The project participants then designed a reference workplace incorporating the measures below:
- Shift from oil-based MCL to emulsion
- Increased feed rates
- Improved lighting in quality assurance
- Improved ergonomics
- Improved communication after work shifts
- Clear responsibilities in filter maintenance
- Elimination of organizational shortcomings
Abbildung 5: Profactor Produktionsforschungs GmbH
The most important modification of the production process consists in the shift to emulsion-based minimum cooling lubrication. Experience has shown that machining with higher feed rates following the laboratory test results, combined with minimum lubrication is feasible in practice. In addition to a reduction of lubricant consumption, the process afforded an improved surface finish and, simultaneously, an equally long tool life.
The chips and machined work pieces are virtually dry and hardly fouled by oil. This facilitates cleaning and quality assurance and also improves recyclability of residue material. Overall, machine operators welcomed all the implemen-ted measures.
Measurements have shown a reduction of mist emissions from approx. 10 mg/m3 to 0.6 mg/m3. A prerequisite for this improvement is that the emulsion application rate is strictly maintained at 2 ml/min. Improved indoor air quality has been noticed and appreciated by employees.
Problems in the process were associated with the emulsion delivery system: It was not possible to en-sure stable adjustment of the twin nozzle in the requisite control range. A permanent shift to emulsion-based lubrication therefore requires the implementation of an specialized delivery system. The follow-up project therefore aimed to develop an improved pump-nozzle system for the minimum cooling lubrication method.
