Development of the machining and surface treatment technology of aluminum parts at Török Gépipari Kft. The R&D project was implemented within the framework of the GINOP-2.1.2-8-1-4-16-2018-00659 application.

1. Development objectives

The aim of this project is to develop technologies that will improve the lifespan of aluminum used in the aerospace industry. Other sectors of the automotive industry are also target areas during the research, as the use of the latest developments in the aerospace environment is increasingly advancing in the automotive industry, as environmental pollution, decreasing fossil energy consumption and more economical operating conditions pose serious challenges.

The lightness of aluminum compared to other metals gives it application opportunities in many places. Aluminum is a light metal, with a specific gravity of 2700 kg/m3. The softness of aluminum can be reduced by making alloys. Molten aluminum mixes with other metals in its molten state, from which it does not separate even after cooling, forming alloys with them. There are more than two hundred aluminum alloys produced today. Among these, there are many that, in addition to their lightness, compete with the hardest steels in strength and hardness. In general, two aspects apply in the production of alloys: on the one hand, they try to increase hardness, and on the other hand, they try to produce alloys whose specific gravity is even lower than that of aluminum. Among the alloys (Duralumin, Silumin, Anticorodal, Fredal, Paraluman, Magnalium, Zimalium, Hydronalium, Alzanfém, Scleron, Aeron, Lautal, Aludur, Montegal, Constructal, etc.), there are those suitable for almost every purpose. Duralumin and Siludur, for example, stand out for their hardness, and among magnesium alloys there is one whose specific gravity is well below that of aluminum. These alloys are used in the construction of aircraft frames and parts generally exposed to high forces. Parts where high strength is not required are made of lightweight magnesium-aluminum alloys. Such an alloy is the so-called "electron metal" (90-95% magnesium + 2-5% zinc + 3-5% aluminum), whose specific gravity is much lower than that of aluminum. The propeller, wing surface and outer coverings are made of this. Zeppelin airships are made of a very special alloy, ZZ-metal. This alloy can be colored using a special process and used to make tasteful ornaments.

A wide variety of types of malleable alloys are also used. The installation location and the given use determine the type. Different alloys are required for a load-bearing element and different ones for a covering, where aesthetics play an important role, among other things.

The processing methods of alloys are also extremely diverse, such technologies include sheet metal forming, cold and hot forming (pressing, forging, deep drawing, etc.) and machining.

During the development, the machining of these alloyed aluminums by machining is being developed, such as its machining, preparation for surface treatment, surface treatment and coloring (anodizing), and then post-treatment of aluminum oxide surfaces with laser marking and engraving.

Török Gépipari Kft. has a modern machinery park, the plant includes, among other things, the most common equipment of individual and small-series production plants, such as CNC lathes, 3-4-5-axis CNC machining centers, CNC wire EDM, CNC surface and surface grinding machines. The physical implementation of the project, production tests were carried out with the company's own equipment, involving their highly qualified cutting and surface treatment specialists.

The Company's customers come from many different industries, such as aerospace, military, automotive, agricultural, food, industrial automation, special machinery manufacturing, etc., each of which poses serious challenges at different levels in terms of the best possible quality, deadlines and competitive prices. The company operates with a committed quality-centric approach, thanks to which, in 2006, a quality management system compliant with the MSZ EN ISO 9001 standard was introduced as a first step. Subsequently, an integrated quality management and environmental management system was introduced and applied, which complies with the requirements of the MSZ EN ISO 9001:2015 and MSZ EN ISO 14001:2015 standards. The company also regularly conducts external customer audits, which are often conducted according to the VDA automotive industry standards, which are even stricter than the above.

To support production, an advanced measuring room has been set up, where they can also check the full range of components manufactured in the plant. This is also where the industrial, high-performance laser engraving machine is located, which is now an indispensable tool for labeling manufactured products and providing them with a company logo for later identification.

2. Overview of tasks related to research and development activities

The development of machining processes is an integral part of the research project.

The development of innovative surface treatment and machining services was implemented through the following R&D project activities:

• Development of machining technology for typical automotive component materials and component groups. Determination of optimal machining parameters, development of type technologies for typical component groups.
• Investigation of aluminum surface treatment technologies by analyzing porosity homogeneity and wear resistance values.
• Development of surface preparation, anodizing technology, determination of technological window.
• Post-treatment of aluminum oxide surfaces by laser marking and engraving.

The machined parts manufactured in the factory and integrated into the vehicle

3. Summary of research and development activities

3.1. Development of cutting technology for typical automotive component materials and component groups. Determination of optimal cutting parameters, development of type technologies for typical material and component groups.

The most commonly used materials are EN AW 2017 from series 2, EN AW 5083 and 5754 from series 5. EN AW 6061 and 6082 from series 6 are also frequently used materials in the automotive industry, and series 7 (EN AW 7021, 7022, 7075), which is considered one of the best, is also a relatively important player, mainly due to its good mechanical properties.
The cutting of aluminum alloys differs significantly from the machining of steels, and extremely high rotational speeds may be required, depending on the tool diameter. In general, for machining aluminum alloys, a cutting speed range of 150-500 m/min and a feed rate of 0.05-0.2 mm per tooth are recommended according to most technical literature.
Sharp tools are required for material removal, and due to the high cutting speed, the amount of removed chips is also significant, therefore its efficient removal must also be taken into account when selecting tools.
In the technical literature, the intervals for individual cutting parameters range quite widely, therefore more accurate values ​​can be determined experimentally.
In this project, the cutting of aluminum alloys most commonly found in the automotive industry was investigated, and their characteristics are listed in the table below.

Characteristics of the aluminum alloys studied

A 3-edged, 16 mm diameter ATORN 11263317 carbide milling tool, specifically developed for aluminum machining, was used for the experiment.

The milling tool used in the experiment

Cutting experiments on various aluminum alloys were performed using the recommended cutting parameters. The parameters were varied in the cutting speed range of 150-500 m/min and the feed rate range of 1200-4500 mm/min.

The test was performed on rectangular bodies of the same size, with the cutting speed increased per side (150, 267, 384 and 500 m/min) and 4 different feed rates (1200, 2300, 3400, 4500 mm/min) applied, resulting in a total of 16 samples for each aluminum alloy.

The quality of the surface formed on the different strips formed on the cut pieces was examined using a Mitutoyo SJ-301 surface roughness measuring device. 3 measurements were taken on each strip in order to record accurate values.

The Mitutoyo SJ-301 surface roughness tester used for the test

The average surface roughness values ​​for the different cutting parameters were plotted in a diagram, and then the trend line fitted to the points was used to approximate the expected roughness values ​​with increasing cutting speed.

In the case of EN AW 2017 alloy in the entire test range:

• With a feed rate of 1200 mm/min, average surface roughness values ​​below 1.5 µm were measured in the entire tested cutting speed range.
• With a test value of 2300 mm/min, a nearly constant surface quality was observed above a cutting speed of 300 m/min.
• With a rough approximation at feed rates of 3400 and 4500 mm/min, a linear decrease can be observed with increasing cutting speed.

Evolution of surface roughness of EN AW 2017 alloy with increasing cutting speed

The next test material is the EN AW 5083 and 5754 materials belonging to the 5 series, which were tested in comparison with each other.

• The best average surface roughness achieved varies around 1 µm. According to the test data, this requires a cutting speed of at least 370 m/min at a feed rate of 1200 mm/min, above which the surface quality does not change significantly.
• Similar quality can be achieved even with a feed rate almost doubled (2300 mm/min), if the cutting speed is increased to 410-420 m/min.
• At a feed rate of 3400 mm/min, the surface quality improves steadily from 280 m/min, with increasing cutting speed.

Evolution of surface roughness of EN AW 5xxx alloys with increasing cutting speed

6-series materials

In these cases, almost the same average surface roughness was measured at the lowest feed rate tested above 350 m/min cutting speed.

With a feed rate of 2300 mm/min, the measured values ​​were more favorable for the EN AW 6082 material, while in the case of the EN AW 6061 material, above 400 m/min, the average surface roughness began to deteriorate in an unusual way with increasing cutting speed.

The best surface was obtained at a feed rate of 2300 mm/min, and the measurement results were obtained between 360-390 m/min.

With feed rates of 3400 and 4500 mm/min, curves running almost parallel to each other were obtained, with the only difference being that in the case of 4500 mm/min, above 400 m/min cutting speed, almost the same Surface roughness (~2 µm) is observed.

Evolution of surface roughness of EN AW 6xxx alloys with increasing cutting speed

Series 7 alloys

For EN AW7021, 7022, 7075 materials, the average surface roughness is approximately 1 µm at a cutting speed of 350 m/min at a feed rate of 1200 mm/min.

By increasing the feed rate to 2300 mm/min, the average surface roughness value decreases almost linearly with increasing cutting speed up to 400-420 m/min, then the values ​​also stabilize between 1-1.5 µm.

At a feed rate of 3400 mm/min, the surface qualities of EN AW 7021 and 7022 alloys developed similarly, the best value is expected between 280-300 m/min, then it becomes constant above 400 m/min. the average surface roughness developed.

For EN AW 7075 material, the surface quality improved almost linearly with increasing cutting speed. At the highest feed rate tested, 4500 mm/min, the aforementioned linear decrease can also be observed in the case of all three alloys.

Evolution of surface roughness of EN AW 7xxx alloys with increasing cutting speed

Summary

Summing up the values ​​examined in the above paragraphs, the cutting parameters are as follows.

It can be stated for each alloy that the best surface quality (~1 µm) was obtained in the range between 340-500 m/min and with parameters of 1200 mm/min.

At a value of 2300 mm/min and a cutting speed range of 420-500 m/min, surface roughnesses between ~1-1.5 µm were measured.

In the case of feed values ​​of 3400 and 4500 mm/min, it can be said that for almost all alloys, an almost linear decrease can be observed in the average surface roughness when increasing the cutting speed. The EN AW 6061 and 6082 materials are an exception to this, as in that case, at a feed rate of 4500 mm/min, an almost constant average surface roughness of around ~2 µm was obtained from 400 m/min.

The table below summarizes the values ​​determined based on the conducted experiment and considered optimal. (The feed rate used during the experiment was converted to feed per tooth.)

During the research, it can therefore be determined which cutting parameters are appropriate for which materials, and the data is made openly available.

Measurement data