Optical profile grinding machines are widely used in modern manufacturing processes, also known as PG (Profile Grinder), which is a high-precision machining process. The processing accuracy can reach an accuracy within 1μm, and the surface roughness can reach Ra0.01μm. Suitable for form grinding of high hardness materials, such as workpieces made of tungsten steel or carbide. Generally, workpieces such as blades and punches, terminals, precision half-stroke punches, lower die inserts and stripper plate inserts are used for processing connector dies.

A ball can be thought of as a curved surface formed by an arc rotating about its axis. Due to the complex curved surfaces of ball head parts, CNC processing is usually used to ensure size, position accuracy and surface quality requirements. With the continuous improvement of machine tool performance and tool materials and performance, ball head parts with ball head diameter ≥8mm and material hardess ≤64HRC can be processed using traditional methods, including: 

① CNC using omnidirectional turning tools or cycloidal tools Lathe processing. 

② Use whirlwind milling which requires extremely high tool position adjustment. 

③ Form grinding using a special grinding wheel dressing device. 

④Grinding using the generation method of a customized cup-shaped grinding wheel. 

⑤ Use special grinding blocks for filing processing in mass production (only hemispherical shaft ends with regular shapes can be processed).

Features of micro ball head parts: 

① There is a curved ball head structure at the shaft end, which is divided into small hemispherical surface, hemispherical surface and large hemispherical surface structure, as shown in Figure 1, with a hardness of about 60HRC.

②The ball head diameter is small, generally the ball head diameter is ≤3.5mm. 

③ During processing, the transition section of the ball head is easily broken by radial force. 

④The size of the parts is small, and the tool structure has a greater impact on the processing of the workpiece.

⑤It is difficult to dress the forming grinding wheel.

It can be seen from the characteristics of micro ball head parts that it is insufficient to use traditional processing methods to form micro ball heads at the shaft end.

For a small number of tiny ball-head parts with general precision requirements, rough engraving and milling in a soft state can be achieved, followed by polishing after heat treatment. However, for tiny ball-head parts with higher precision requirements, more suitable processing methods still need to be found.

Since it is difficult to achieve precision hard machining of tiny ball head parts and it is not easy to achieve batch processing, the formation mechanism of the shaft end ball head (making the bar rotate at high speed to form the ball head in the form of an arc envelope) and the equipment Based on the processing principle, a processing method for large hemispherical ball head parts with small shaft ends is proposed: special tooling is made to rotate the rod at high speed, and the processing principle of integrating points into lines with an optical profile grinder is used to process the ball head in the form of an envelope. Precision forming processing of the head.

Optical profile grinder processing method

The optical profile grinder is mainly composed of a bed, a coordinate workbench, a grinding wheel table and a projection system. The workbench can move longitudinally, transversely and vertically; the grinding wheel can make main rotational movements and at the same time make linear motion on the guide rail of the grinding wheel table; the grinding wheel The table can perform longitudinal and transverse feed movements as well as rotation around the X/Y/Z axis. It can realize grinding of multi-arc surfaces, logarithmic surfaces or Archimedean spiral surfaces.

Optical profile grinder processing uses an optical projection amplification system to enlarge the workpiece and project it onto the screen, and compare it with the enlarged picture of the workpiece on the screen. During processing, the grinding wheel is used to grind the workpiece, and the excess material that exceeds the outline of the enlarged picture is ground away. , until the outline of the object image completely coincides with the enlarged image. Can be magnified 25 times and 50 times for comparison. The structural types of diamond grinding wheels used in optical profile grinders include flat grinding wheels, pointed grinding wheels, etc.

According to the structure of the grinding wheel used in the equipment, it can be seen that using an optical profile grinding abrasive layer tip grinding wheel in conjunction with a digital control system can achieve curved surface grinding with a diameter of ≥0.2mm. If it cooperates with the rotation of the workpiece, the forming processing of the corresponding curved surface of revolution can be realized.

The processing of this part has the following difficulties: 

① The ball head requires high dimensional accuracy and the shaft diameter of the part is small. 

②The diameter of the ball head transition section is only 1.2mm, the processing rigidity is low, and it is easy to break under stress. 

③The machining allowance is large, and the requirements for processing technology, convenience of clamping, stability and radial runout of bar rotation are relatively high.

④The quality requirements for the surface roughness of the ball head are relatively high.

If an optical profile grinder is used to achieve precision forming processing of the ball head rod, special tooling must be produced to ensure that when the grinding wheel moves along the contour of the workpiece, the ball head rod rotates around the axis to form a ball head structure. Due to the small size of the ball head rod, if the grinding wheel reciprocates up and down along the grinding wheel frame, the effective contact time between the grinding wheel and the rotating workpiece will be reduced. Therefore, in order to improve the processing efficiency, the height position of the grinding wheel is adjusted and fixed during workpiece processing, and the grinding wheel is eliminated. The reciprocating motion along the grinding wheel frame makes the grinding wheel always in effective contact with the workpiece surface when rotating. The grinding wheel only moves along the forming contour line when rotating at high speed. Taking into account the number of workpieces, the ball head rod and the grinding wheel structure, since the sharp grinding wheel fillet is small and the processing loss is large, in order to reduce the loss of the sharp grinding wheel and improve the processing efficiency, a flat grinding wheel is used to process when removing a large margin, and the process is processed step by step. The process of formulating the ball head rod processing technology is as follows:

1) Use a flat grinding wheel to roughly machine the ball head rod, leaving a margin of 0.02mm for sections A and B, and a margin of 0.1mm for section C. The grinding wheel translation speed is 3mm/min, and the grinding wheel speed is 12000r/min.

2) Use a sharp grinding wheel to process the ball head rod profile, control the dimensional accuracy during processing of sections A and B, leave a margin of 0.01mm in section C, the translation speed of the grinding wheel is 1.5mm/min, and the rotation speed of the grinding wheel is 12000r/min.

3) Use a sharp grinding wheel to fine-tune the C-section ball head. The grinding wheel translation speed is 0.5mm/min and the grinding wheel rotation speed is 12000 r/min.

Processing effect detection

The ball head rod is processed in steps. Since the flat grinding wheel has an automatic grinding function, the surface quality of the processed cylinder is better; the pointed grinding wheel is mainly responsible for finishing, with a small machining allowance and small grinding wheel loss. During the processing of 500 ball studs, the sharp grinding wheel was dressed 4 times. It can be seen from the test results that the ball head rod processed by this method meets the design requirements.

Due to its own structural characteristics, micro ball head parts cannot be processed using traditional shaft end ball head parts. An optical curve grinder is used with homemade special tooling, and a step-by-step processing process is designed. The radial force is small during the processing of the ball head rod, and the transition section is not easy to break. This grinding processing method well solves the processing problems of small-sized ball head parts, and has the advantages of high qualification rate, simple operation, controllable processing accuracy and good product consistency.

Moresuperhard have resin and metal diamond optical profile grinding wheel for precise grinding mould and die, punch pin, optical grinding and form grinding cutting tool ( such as end mill and reamer) and precise instrument.

---EDITOR: Doris Hu

---POST: Doris Hu