Superhard material guide reamer repair

Superhard material guide reamer repair

Abstract: Based on the repair test of MAPAL reamer guide strip, this article discusses the theory and practice of grinding superhard material guide tools, which has guiding significance in the grinding process of imported high-value tools.

Superhard tools are mainly made of diamond and cubic boron nitride. Among them, synthetic diamond composite (PCD) tools and cubic boron nitride (PCBN) tools are dominant. Superhard tools have the characteristics of high work efficiency, long service life and good processing quality, and are recognized internationally as one of the most promising tool materials for improving productivity. There are many types of tools, including turning tools, milling cutters, boring cutters, drills, taps, planers and reamers, etc. Various types of tool manufacturers are also different, including MAPAL, WALTER, SECO and OSG, etc. The reaming process uses MAPAL imported tools, which are advanced in design and expensive. After the tool is used, if it is no longer repaired, it will cause a very large waste and increase the manufacturing cost.

 

1. Super hard tool structure

This article takes the reamer as an example to introduce the superhard tool structure.

At present, the use of super-hard tools is mainly embodied in the reamer used to process the cylinder head valve guide. This reamer is mainly composed of five parts. The first part is the shank, which is the clamping part, which is clamped by the tool holder and installed on the machine tool. The second part is the guiding part. The guiding part is inlaid with superhard materials. The inlaid superhard materials are used as the guide. The superhard materials mainly include CBN composite sheets and PCD composite sheets. The diameter of the guide part is usually smaller than the diameter of the cutting part 0.003~0.005mm . The third, fourth and fifth parts are close together, including the pressing part of the third part, the adjustable part of the fourth part and the blade part of the fifth part. The third part is compressed by a compression screw to press the blade In the blade slot, it plays a role of fixing the blade. The fourth part is an adjustable part, which also includes an adjustable screw and an internally installed adjustment pin with a bevel. Generally, the adjustable part can adjust the blade by 0.01~0.02mm. Extend the service life of the blade. The fifth part is the blade part. This part participates in the processing of parts. The processed metal is usually CBN blades, and non-metal is usually PCD blades. Because PCD has an affinity with carbon, it cannot be used for steel and steel metal processing containing carbon elements.

 

2. Current status of tools used

The three types of reamers currently used in our factory are mainly Φ11mm short reamer, Φ9mm reamer and Φ11mm long reamer, which are mainly used in processing centers manufactured by Toyota and special machines manufactured by Dalian Machine Tool Plant. The processed products mainly include two-valve cylinder heads and four-valve cylinder heads. 

 

Current situation of tool use
No.	Cutting tools	Specifications	Factory	Price/RMB
1	Reamer	4-27215-165849	MAPAL	20459
2	Reamer	9-27915-15415	MAPAL	20403
3	Reamer	9-27915-15416	MAPAL	19487

3 types of reamers are currently in use.

Φ11mm short reamer is mainly used in machining centers to process two-valve cylinder heads ;

Φ9mm reamer is mainly used to process four-valve cylinder heads;

Φ11mm long hinges The knife is mainly used on special machines to process two-valve cylinder heads.

 

 

At present, MAPAL reamer is used for the catheter valve seat of the gun reaming cylinder. Through multiple repair tests, it is concluded that the repair of the guide strip mainly includes the following processes: clean the damaged guide strip and the compression screw from the reamer → clean the guide strip groove → measure the size of the guide strip → cut the PCD or PCBN composite sheet → Grind the guide bar to the required thickness → weld the guide bar to the reamer → grind the outer circle of the guide part of the reamer to meet the size requirements → assemble the tool.

 

3. Guide strip repair process

The repair process of the guide bar is carried out according to the processing technology standard (process card), and the protection measures should be paid attention to during the processing.

(1) The fitter process. The fitter process is mainly to remove the guide bar and the compression screw after receiving the repair reamer. During this process, pay attention to protecting the threads of the compression screw groove, to prevent the guide from being burned out at high frequency in the next step The welding slag destroys the thread during the stripping process. Press the screw and the pressing block to compress the blade, remove the screw and the pressing block during high-frequency welding, and plug the threaded bottom hole with small paper scraps to prevent welding slag from entering. After welding, tap the thread with a tap to ensure The compression screw is easy to install.

 

(2) Wire cutting process. The wire cutting process is mainly based on the measured guide strip size, cutting the appropriate size guide strip from the PCD and CBN composite sheet. PCD and CBN composite sheets are generally discs.

The CBN composite sheets used to repair the guide bar of the reamer are discs of φ58mm×2.0mm and φ58mm×3.2mm, imported materials purchased from Shanghai blue-collar manufacturers.

 

PCD and CBN cutter for Guide strip grinding
No.	Name	Specifications	Quantity	Remarks
1	CBN cutter	φ58mm*2.0mm	2Pcs	Import
2	PCD cutter	φ58mm*3.2mm	2Pcs	Import
3	PCD cutter	φ74mm*2.8mm （grit 25μm）	1Pcs	Import

(3) Sharpening process. The tool and die workshop uses the PCD blade welding process when repairing the German MAPAL reamer guide strip used in the No. 1 plant. The blade thickness is required to be 1mm, but the thickness of the purchased blade is 3.5mm. This requires that the purchased blade be placed on the universal tool grinder. Grind up to 1mm. When grinding PCD blades, stick the blades on the grinding plate and grind them with the side of a diamond bowl wheel. However, because of the long processing time and low grinding efficiency, the lead time cannot be met. The time survey table for each step of the sharpening process.

 

Questionnaire for each step and time of the sharpening process
No.	Step	Time/s	Percentage/%	Cumulative percentage
1	Grinding	20	57.1	57.1
2	Card mount	5	14.3	71.4
3	Straighten	4	11.4	82.8
4	Measure	2.5	7.1	89.9
5	Special inspection	1	2.9	92.8
6	Tooling	1	2.9	95.7
7	Dressing the wheel	1	2.9	98.6
8	Install the wheel	0.5	1.4	100
Total		35	100

Originally, glue was used to bond the composite sheet to the ground square iron during grinding. This method has the following disadvantages:

① Because the force of the glue is not strong enough, the feed cannot be large, otherwise it will Make the composite sheet fly out.

② Grinding cannot be continued, otherwise, as the temperature becomes higher, the glue will lose its viscosity and cause the composite sheet to fall off.

③When measuring, use a dial indicator to measure the thickness difference between the square iron and the composite sheet, and calculate the thickness of the composite sheet. The measurement is inconspicuous and unintuitive.

 

After the improvement, the composite sheet is clamped with precision pliers and ground with a disc-shaped grinding wheel, which can achieve large feed and continuous grinding. The comparison measurement of the meter block improves the measurement efficiency and accuracy.

 

(4) High frequency welding process. The welding of PCD and other composite sheets requires silver soldering pieces. There are many specifications of silver soldering pieces. The following is a part of the introduction: DHAg-35B Melting temperature: 607°~702°, suitable for heat exchanger welding. DHAg-30B Melting temperature: 677°~766°, the melting point is slightly higher, the joint has good toughness, and can be brazed for copper, copper alloy and steel materials. DHAg-25B Melting temperature: 700°~800°A low-cost cadmium-free solder, good wettability and filling ability, but high melting point, can braze copper, copper alloy, steel and other materials. Through consultation and verification, the appropriate silver solder sheet and silver flux were selected. In addition, the temperature of the composite sheet cannot exceed 700° during welding.

 

Silver solder for Guide strip grinding
No.	Name	Specifications	Quantity	Factory
1	Silver solder blade	DHag-50	1kg	Shanghai
2	Silver solder	Qj305	1kg	Shanghai

 

(5) External grinding process. When grinding the guide bar in the external grinding process, due to the high hardness of the guide bar, the diamond grinding wheel used for grinding cemented carbide cannot be ground, and the vitrified bond diamond grinding wheel must be used. For this purpose, a customized grinding wheel is purchased.

diamond grinding wheel for Guide strip grinding
No.	Name	Specifications	Quantity	Remark
1	Vitrified diamond grinding wheel	EA1 φ400mm-40mm 203-6 W20 100%	1Pcs	Import

 

 

4. Conclusion

The repair of various CBN blades saves at least 300,000 yuan in costs for the company every year. The successful repair of the tool bar saves the company at least 500,000 yuan every year. The repair of such tools saves costs while reducing the company's inventory of such tools and blades, shortens the outsourcing cycle, and provides a guarantee for the company's production.