Manufacturing technology of small-sized profile parts

. The paper considers the issues of processing small-sized profile parts, in particular, micro milling on a contour-milling machine with CNC. The technology of fixing small parts due to the adhesive connection is proposed. Calculations of the adhesive joint are carried out taking into account the coefficient of safety margin for shear resistance. Experimental studies of contour milling processing were also carried out, as a result of which recommendations were formulated on the choice of processing modes for copper alloy 99.5%Cu. The tool breakage limit is determined under the specified processing conditions. The possibility of using a combination of micro milling and electroerosion treatment is considered.


Work actuality
With the development of production, many devices become more compact and more complex in structure.This leads to a reduction in the size and complexity of the geometric shape of the components of the product.This is especially true for medical devices [1], electronics and aircraft construction.The main problem of processing small-sized parts is the method of fixing them on the workspace, since small overall dimensions often do not allow the use of traditional methods of fixing.Based on this, the task arises in the search for new technical solutions, methods of fixing and methods of processing small-sized parts.In this regard, microprocessing is relevant for many researchers [2][3][4][5].
When forming small-sized parts, it becomes difficult to select methods and technologies that meet the specified manufacturing requirements.Therefore, the task of finding new and upgrading existing methods for obtaining small-sized parts is urgent.

Theoretical part
One of the main problems in the machining of small-sized profile parts on milling machines is the complexity of their geometric shape.The complexity of the design leads to the need to use special equipment or increase the number of installations, which leads to an increase in error and an increase in the final cost of manufacturing.Also, the main problem that arises when machining small-sized parts is the difficulty of bringing the tool to the surfaces to be processed due to the limited working space.Due to the small overall dimensions, it is not always possible to supply the cutting tool, since the space for moving the tool is limited by the surfaces of the technological means used.The method of fixing them on the workspace due to the small overall dimensions of the parts is most often associated with an increase in processing time and cost, which in turn are associated with an increase in the number of installations or the manufacture of complex specialized equipment.For the manufacture of small-sized profile parts, depending on the available equipment, a large amount of technological equipment may be required.Also, one of the important aspects in the manufacture of small-sized parts is the supply of tools to the surfaces to be processed, which causes great difficulties with classical fastening methods.
In addition to mechanical processing, electrochemical, electrophysical and laser processing methods have recently been used to solve technical problems of small-sized profile processing.Each of these methods has its advantages and disadvantages, the totality of which, in a modern economy, in conditions of high competition, determines the choice and application of one of them.
At the initial stage of production, the manufacturability of the part is analyzed, which reflects the degree of complexity of its processing.Based on the obtained data of the assessment of manufacturability and the features of the manufactured part, the choice of processing equipment and technologies is determined.For example, some technological methods of manufacturing small-sized profile metal parts, namely laser cutting, micro milling, electroerosion treatment, have certain processing advantages.This is due to different principles of action on the workpiece being processed.
Electroerosion treatment with a wire electrode-tool allows you to produce parts of complex geometry due to simple translational motion, as well as operations are performed without the force of the tool on the workpiece, which allows you to cut small-sized parts from the fixed workpiece.With this method, there is no problem of supplying the electrode to the treated surfaces.Along with this, this technology is applicable only to conductive materials, which leads to the impossibility of processing dielectrics.Also, the method is not highperformance and energy-consuming, which causes its high cost.
Laser cutting, as well as electroerosion, does not have a forceful effect on the workpiece being processed, which ensures processing without fixing.The absorption capacity of the metal, which depends on the thermal conductivity, has a significant influence in the manufacture, which also causes limitations in the processing of many metals.In addition, due to the thermal effect, slag may appear on the edges of the manufactured small-sized parts, which in some cases is unacceptable.
Thus, when processing small-sized parts, all of the above methods have their advantages and disadvantages, which can be reduced to the following main points:  Laser and electroerosion machines are a special, narrowly focused, expensive and extremely powerful machine, which in the framework of mass production causes a high cost of manufactured products.At the same time, milling machines are universal, processing on them is low-cost, which is confirmed by research. The milling machine is equipped with a number of various cutting tools designed for various types of cutting and processing of small-sized complex shapes with specified technical requirements [6]. Laser and electroerosive processing methods have limitations on the processing of aviation materials, such as magnesium, which reduces their use in the aircraft industry.When milling, there are no restrictions in the processing of various materials, which is due to the choice of appropriate cutting modes and tools.When comparing electroerosion and milling processing, it was also revealed that micromilling leads to a lower surface roughness than microelectroerosion treatment [7].In terms of processing time and energy consumption, milling also has an advantage.
There are also combined methods of processing small-sized parts, for example, micro milling and electroerosion processing, which allow using the advantages of each of the methods [8].
Based on the above, milling has a number of advantages over electroerosion and laser processing, which explains its greater spread in mass production.
Thus, the task of this work is to search for new technical solutions, methods of fixing and methods of processing small-sized profile parts on CNC milling machines.

The methodology of the experiment
The processing process of a small-sized part (Fig. 1) in the framework of a single production is investigated.The component in question has small overall dimensions, a complex, but flat, geometric shape.The material of manufacture is copper alloy 99.5%Cu.After studying the geometric and technical data of the part, it was decided to manufacture this component on a CNC milling machine.The workpiece is a plate with dimensions equal to 20x20 mm and a thickness of 1 mm.Processing options on a CNC milling machine and a low-power laser center were considered.The high absorption capacity of copper causes difficulties in processing this part with laser technology.The search for standard technological equipment revealed that vacuum or magnetic plates are best suited for milling sheet material.The former will not provide reliable fixation of the cut-out parts, since the contact area is very small, the latter cannot be used due to the nonmagnetism of the material.
Based on the inability to use standard technological equipment, the following manufacturing method was developed.For fixing, a plate 1 is used larger than the workpiece (Fig. 2), the material of which is steel of normal quality.On one of the surfaces, step 2 is milled, which serves as a surface for basing the sheet blank 3 and setting the zero processing point.Glue is applied to the workpiece 3 with a layer of about 0.5 mm for its subsequent fixation on the plate 1.The finished technological means it is installed on the working space of the machine and fixed by means of L-shaped tacks.The orientation of the coordinate system of the tool relative to the coordinate system of the workpiece is performed, and the part 4 is cut out.In this method of fixing, an adhesive joint is involved, the main parameter of which is the magnitude of the destructive force P, during shear.The magnitude of the destructive force is directly proportional to the bonding area, that is, the larger the bonding area, the greater the shear force, in this case the circumferential force during milling, must be applied to destroy the adhesive joint.According to the magnitude of the destructive shear stress, the best indicator is epoxy adhesive, the tensile strength of which can reach from 6 to 14 MPa.When the area of the cut-out part is 14.4 mm 2 , the destructive force is equal to 144 N, this parameter imposes restrictions when assigning cutting modes.The workpiece heats up during processing, which leads to a decrease in the temporary resistance of the adhesive joint.This is excluded by the use of coolant, if its use is possible.
An important aspect of milling with small diameter cutters is the assignment of optimal cutting modes.The development of a control program is also an important aspect in micro milling [9].
The cutting force along a complex trajectory is constantly changing, which can lead to tool breakage and disruption of milling continuity, which increases the final error of the part.To prevent this, the following strategies are used in the CAM systems:  cutting the tool into the part should be as smooth and long as possible.This can be achieved by using an inclined embedding or a spiral embedding from top to bottom;  to achieve uniformity of the tool path, you can use the same strategies as in high-speed processing, for example, strategies for rounding corners and spiral milling.The conducted studies have shown that the strategy by which the best results are achieved is the strategy of the "spiral of constant overlap" [10].
The ZCC CT GM-2E-D1.0milling cutter was used in the manufacture of parts, an inclined embedding at an angle of 2° was used (Fig. 3).This parameter ensures smooth and long-lasting cutting of the tool into the workpiece, which minimizes the change in cutting force.An inclined clearance height of 0.3 mm is also assigned.This is necessary due to the  Cutting modes also have a great influence on the micro milling process, the fundamental difference between micro milling and conventional milling is related to the scale of the operation, despite the fact that it is kinematically the same.However, the ratio of feed per tooth to the milling cutter radius during micro milling is much greater than during conventional milling, which often leads to an error in predicting cutting forces.In addition, the beating of the cutting edge of the tool, even within micrometers, greatly affects the accuracy of milling compared to conventional milling [11].
There is a very narrow limit to the optimal values of feed per tooth and rotational speed when milling small-sized parts with a small diameter tool [12], therefore, the choice of optimal cutting modes is one of the main areas of research in micro milling.In the conducted experiments, the performance parameters of the tool were studied.In studies [6], large forces were observed with a decrease in the diameter of the milling cutter and an increase in the spindle speed.Also, the equipment used has a significant impact on the quality of micro milling.
The method of fixing in question is not reliable.Therefore, when calculating the cutting modes, a safety margin factor of 4 is introduced.Then, under the selected modes, the cutting force trying to destroy the adhesive joint should not exceed 35 N.
The experiment was carried out on a CNC milling machine "Router 6040C" with a maximum rotation speed of 24000 rpm and the full overlap of the milling cutter.The remaining cutting modes were selected experimentally, based on the change in cutting force and the appearance of vibrations during processing.The cutting depths were selected based on the number of passes -0.15 mm (7 passes), 0.25 mm (4) and 0.35 mm (3).

Experimental results and discussion
As a result of the experiments, the following average values were obtained (Table 1).The lack of data in the last lines is due to the fact that the cutters do not withstand such modes and break down.With an increase in these milling parameters, the processing time is naturally reduced, but the cutting force increases, which causes vibrations.Vibrations make it impossible to continue processing.The cutting force Pz = 19 N, which occurs when the cutting depth t = 0.35 mm and the feed S = 575 mm/min leads to a breakage of the cutter.Acceptable values were processing with a cutting depth of 0.25 mm and a feed of 650 mm/min.A further increase in the feed also leads to tool breakage (Fig. 4).With a decrease in the parameters under consideration, the manufacturing time increases, along with this, the processing error increases, due to an increase in the cutting path.Analyzing the data obtained, it can be concluded that with a cutting depth of t = 0.25 mm, the resulting cutting force does not cause vibrations that significantly affect the quality of processing.Also, with this parameter, the processing time is significantly reduced compared to the cutting depth of 0.15 mm and is slightly inferior with a cutting depth of 0.35 mm.
The cutting temperature during processing did not change due to the use of coolant, which does not change the temporary resistance of the adhesive resistance.
Then the best indicators when processing a small-sized part on a CNC milling machine in terms of productivity and quality are: t = 0.25 mm, F = 500 mm/min.
It is worth noting that with this technology there is a method of multiple processing [4], that is, obtaining several parts of different configurations from one workpiece.When using this method, the cut-out parts must be arranged in a CAD system so that when creating a control program in the CAM module, all the surfaces of the elements are accessible to the cutter.

Conclusions
The proposed technology and the proposed equipment make it possible to produce smallsized profile parts, the size of which can reach up to 1x1x1 mm, significantly reduces the time of the technological process, contributes to saving raw materials and labor resources.In addition, this method allows unhindered processing of the part from five sides in one installation, which ensures high accuracy of the mutual arrangement of surfaces.This method of processing is much cheaper and more productive than on electroerosion and laser machines, and there are no restrictions on the processed material in this technology.
The work also revealed the optimal cutting modes for micro-milling of copper with the full overlap of the milling cutter.Graphs of the effect of the cutting depth and feed on the cutting force and processing time are compiled.
It is worth noting that this method is typical for single-production parts and for parts with a flat base.
A further prospect of research in this area is the creation of combined methods for processing small-sized parts, for example, milling-electroerosion or milling-laser processing.

E3S
Web of Conferences 431, 06005 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343106005possibility of irregularities on the workpiece.The totality of the decisions taken reduces the breakdown of the tool to a minimum.

Fig. 4 .
Fig. 4. The dependence of the cutting force P on the feed A during micro milling of copper with a rotation speed of 24000 rpm with a cutting depth of 0.15 mm (1), 0.25 mm (2), 0.35 mm (3).