The application of end mills in the Processing of Automotive Engine blocks

End mills are widely used in the processing of automotive engine blocks, mainly for milling the end faces, top surfaces and other parts of the cylinder block. They have a significant impact on processing accuracy, efficiency and tool life. The following is a detailed explanation:

Processing parts and functions

The engine block is an important part of a car engine. It connects many parts in the machine and components as well as various exhaust pipes into a whole, keeping them in the correct positions and moving in coordination with each other. As the cylinder block is a complex structural component precisely cast, it has high requirements for dimensional accuracy and positional accuracy. The end mill plays a crucial cutting role in the processing of the cylinder block and is mainly used for milling the end face, top surface and other parts of the cylinder block to ensure the processing accuracy of the cylinder block workpiece.

Processing cases and difficulties

Application of large-sized cutting tools: Taking the processing of the top surface of an engine cylinder block as an example, the top surface size is 1062mm×260mm. It is required that there should be no tool marks during the processing of the top surface. Therefore, the diameter of the face milling cutter for processing this surface must be ≥260mm. In the actual processing, a φ315mm face milling cutter with a finishing edge was selected, but the specification of this tool exceeded the tool loading and tool changing conditions of the tool magazine of the machining center.

Optimization of processing plan To achieve automatic tool changing for large-sized milling cutters, the tool rest can be placed on the left side of the worktable and fixed properly. Then, a check bar for alignment can be installed on the tool rest, and a probe can be installed on the machine tool spindle to align the center position of the check bar. The detected values can be written in the machine tool coordinate system to determine the tool changing point position. Finally, this tool can be programmed in the processing program just like other tools. When machining the top surface of the cylinder block part, the spindle will remove the milling cutter used for machining the top surface of the machine body from the tool rest according to the programmed processing procedure, thereby achieving the automatic tool changing of large-sized milling cutters.

Tool selection and installation

Tool selection: To meet the needs of the automotive industry, tool manufacturers have launched a series of milling cutters and inserts for milling cast iron and other materials. For example, Kieninger, a subsidiary of LMT Group, has developed a new type of high-speed face milling system – the Feed-Jet high-speed face milling system. Its features such as dense tooth design (cutter head diameter 125mm, standard configuration of 18 teeth), rack-type clamping structure and steel cutter head are suitable for rough and finish milling of aluminum alloys. By replacing it with a CBN cutting edge, It can also achieve fine processing of cast iron.

Tool installation: Most end mills used in CNC machining centers are clamped by spring clamps and are in a cantilever state during use. During the milling process, the end mill may gradually extend out of the tool holder or even completely fall off, resulting in the scrapping of the workpiece. The general reason for this is that there is an oil film between the inner hole of the tool holder and the outer diameter of the end mill shank, causing insufficient clamping force. Therefore, before clamping the end mill, the shank part of the end mill and the inner hole of the tool holder should be thoroughly cleaned with cleaning solution, dried and then clamped. When the diameter of the end mill is relatively large, even if the tool holder and the tool holder are very clean, a tool drop accident may still occur. At this time, a tool holder with a flattened notch and the corresponding side locking method should be selected.

Processing problems and solutions

The problem of knife marks

The causes of occurrence: The main locations where tool marks appear include the junctions of two tool passes, the areas where the tool passes through the machined surface again during the feed process along the machining path, and the positions where the tool teeth enter or exit the workpiece, etc. The generating conditions include unreasonable cutting parameters (such as large machining allowance and fast feed rate), tool installation errors, tool wear, and the workpiece not being clamped properly, etc.

Solution measures: Select experienced tool adjustment staff who have received professional tool adjustment training to ensure the quality of tool adjustment. Optimize the cutting speed. Select the most suitable cutting speed based on the different components being processed. If the cutting speed decreases, adjust the feed rate simultaneously. Ensure the clamping force of the workpiece to prevent it from loosening.

Edge collapse problem

Cause of occurrence: In cast iron processing, tool wear will lead to an increase in the lateral cutting force. At the moment when the milling cutter head is about to cut out the workpiece, the last bit of machining allowance remaining on the workpiece will be squeezed out, thus causing chipping. The earlier the tool wears, the greater the probability of chipping occurring.

Solution: Reduce the cutting speed. According to the principle of metal cutting, within the reasonable speed range, the cutting speed can be reduced by 20% and the tool life can be increased by 50%. Adjust the feed rate to make up for the deficiency of the rhythm; Optimize the structure of the tool head, such as changing the main deflection Angle of the tool head to reduce the cutting force when the tool leaves the edge of the cylinder block.

Tool vibration problem

Cause: Due to the tiny gap between the end mill and the tool holder, the CNC tool may vibrate during the machining process. Vibration will cause the cutting depth of the circumferential edge of the end mill to be uneven, and the cutting allowance will increase compared to the original value, affecting the machining accuracy and the service life of the tool.

Solution: Reduce the cutting speed and feed rate. If significant vibration still exists after both have been reduced by 40%, consider reducing the depth of cut. If resonance occurs in the processing system, it may be caused by factors such as excessive cutting speed, insufficient feed rate, inadequate rigidity of the tool system, insufficient workpiece clamping force, as well as the shape of the workpiece or the clamping method of the workpiece. At this time, measures such as adjusting the cutting parameters, increasing the rigidity of the CNC tool system, and raising the feed rate should be taken.