The pattern of the tire mold is inherently complex and changeable, and with the major tire manufacturers in order to improve competitiveness, have increased the complexity of the tire pattern and the requirements of the tire mold, the tire pattern changes quite quickly, the variety is diversified, the mold delivery time is also getting shorter and shorter. In the process of using high-speed CNC machining to process the tire pattern, it is often necessary to quickly make process adjustments according to the special structure of the mold pattern cavity, which brings troubles to the technicians. Therefore, in view of the particularity of the tire pattern and the regularity that can be followed, we analyze the processing technology problems and make relevant optimization, so as to improve the processing efficiency.
　　
CNC machining and traditional processing have a unique processing technology, tire pattern CNC machining is no exception, the following on the tire pattern CNC machining process, processing characteristics and process optimization and other issues for a simple analysis.
　　
Process Analysis of Tire Pattern Structure
　　
Those who are familiar with the structure of the tire mold and its processing know that the structure of the inner cavity of the tire pattern block conforms to the characteristics of CNC machining, namely:
　　
(1) The inner cavity and shape of the block have a unified or approximate structure and size. This structure can reduce tool specifications and the number of tool changes, make programming convenient, and improve production efficiency.
　　
(2) Although the tire pattern shape is ever-changing, many patterns have rounded corners, which are suitable for direct processing with cutting tools.
　　
(3) mold pattern block, processing can use its back as a unified reference positioning, in order to ensure that the accuracy is relatively accurate after multiple clamping processing.
　　
(4) There is a suitable hole on the back of the pattern block as the positioning reference hole, or there is a positioning boss as the unified reference, which is to complete all processing positions after the pattern block reaches one clamping, thus improving its processing rigidity and processability.
　　
Process Characteristics of Tire Pattern NC Machining
　　
In principle, there is no difference between the CNC machining of the tire pattern and the regular CNC machining, and the principle of traditional machining is basically the same. But because the tire pattern has its special structure, it has its own characteristics:
　　
Multi-radian multi-angle characteristics, only the use of CNC machining to ensure accuracy
　　
The tire pattern has the characteristics of many radians and many angles (see Figure 1), which cannot be completed by traditional processing methods. Even if the current popular EDM process is used, there are some unsolvable problems, such as the inability to solve each position to maintain the direction. The processing problem, not to mention the common CNC machining such as three-axis or four-axis.
　　

Fig. 1 Tyre Mold Pattern Block
　　
Process is highly concentrated, suitable for CNC machining
　　
In the process of tire pattern processing, the processing process is highly concentrated, mainly milling, but because the processing angle, corner, etc. are not uniform, some patterns have thin and high small ribs or narrow and deep small grooves, Even the surface is irregular potholes, so its requirements for cutting tools are relatively high. The five-axis CNC machining center usually carries a tool magazine and has the function of multi-dimensional conversion, which can complete automatic tool change, realize process compounding, and achieve a high degree of concentration of processes.
　　
Characteristics of CNC Machining Applied to Tire Mold
　　
(1) The processing time of the workpiece is shortened. For the pattern ring of a pair of tire molds, it takes 30 days to use casting technology and 20 days to use electric spark technology. If the use of high-speed processing of direct engraving mold, generally 10 days, it can be seen that the processing time can be greatly reduced.
　　
(2) The workpiece can be roughed or finished after a clamping, and the processing of the pattern corner is more flexible. Tire patterns are mostly small blocks, especially many corners, with a five-axis machining center only one clamping can be carved out of all patterns.
　　
(3) due to the reduction of cutting force and cutting temperature, the tool wear is reduced and the service life is prolonged. The cost of the tool occupies a certain proportion in the cost price of the workpiece processing.
　　
(4) CNC machining can be achieved by cutting grinding. The cutting process instead of the grinding process has the advantages of simplified tool structure, strong process flexibility, energy saving and so on, which makes the processing cost of the workpiece lower.
　　
(5) Compared with the regular processing technology, the processing procedure can be simplified to reduce the processing cost. Such as mold cavity processing, with the regular processing technology is: blank annealing-rough machining-quenching and tempering treatment-semi-finishing-electrode machining-EDM-artificial polishing. The use of CNC machining technology, the processing technology can be simplified as: blank annealing-rough machining-quenching and tempering-finishing-super finishing. In this way, the processing process of electrode production is omitted, the production cost is reduced, the surface hardening problem caused by the discharge machining is eliminated, and the artificial finishing is reduced or eliminated.
　　
(6) improve the processing quality. Because the excitation frequency of the cutting tool is far away from the natural frequency of the process system, it will not cause the forced vibration of the process system, and ensure a better processing state. Because the cutting depth, cutting width and cutting force are very small, the deformation of the tool and workpiece is small, the size is maintained, and the cutting damage layer is thin, the residual stress is small, and the high precision and low roughness machining are realized. From the perspective of dynamic analysis of the formation of frequency, we can see that the reduction of cutting force will reduce the amplitude of vibration (I. e. forced vibration) caused by cutting force; the increase of speed makes the working frequency of the cutting system far away from the natural frequency of the machine tool, so as to avoid the occurrence of resonance. Therefore, CNC cutting can greatly reduce the surface roughness and improve the processing quality.
　　

Fig. 2 Tire Pattern Mold
　　
Optimize process, rate increase
　　
Selection of cutting tools
　　
In CNC machining, the correct choice of CNC tool holder, tool is very important. The general requirements of CNC cutting tools is easy to install and adjust, good rigidity, high precision, good durability, on the basis of comprehensive consideration of the cutting performance of the workpiece material, the processing capacity of the machine tool, the type of CNC machining process, the amount of cutting and many factors related to the working range of the machine tool and CNC device.
　　
For the CNC machining of tire molds, in order to shorten the production cycle and reduce the processing cost, we have selected the following tool holder systems that are more suitable for high-speed machining in CNC engraving (Figure 3-Figure 7).


　　
Figure 3 is suitable for high speed machining of the shank system elastic jacket and heat shrinkable shank. Elastic jacket, this clamping system is currently more popular. Due to its high cost performance, it is widely recognized in the European, American and Chinese markets. Although its price is higher than that of PG/TG elastic jacket, it is suitable for high-speed cutting because of its high precision. The advantages of this system are: good concentricity; relatively small body diameter; large clamping force; a balanced nut system is required; different types of sealing rings.
　　
The heat-shrinkable shank adopts new technology and design. Although it has certain requirements for the clamping tool and special equipment, it has the following characteristics, so it is favored by more and more users in some fields, especially in the mold industry. Its advantages are: good concentricity; relatively small body diameter; low centrifugal force; uniform material; large clamping force; high dynamic balance; body heat treatment; heating system.
　　
High precision HP(HighPrecision) jacket, using new technology and design. Although it is similar to the ER elastic jacket, the clamping method is through positioning instead of thread, its accuracy can be increased by 3 times, and its price is lower than that of hydraulic jacket. The main advantages of the jacket are: good concentricity, large clamping force, small body diameter, easy cleaning, small centrifugal force, easy to do dynamic balance.
　　
The hydraulic tool holder adopts new technology and design. Due to the use of hydraulic technology, so convenient loading and unloading, accurate positioning. Its advantages are good concentricity, small body diameter, easy cleaning, convenient disassembly, etc.
　　
For the aluminum material of the pattern block, processing when we choose the tool is taking into account the efficiency and cost, mainly using the thread milling cutter (Figure 6), its main advantage is the chip removal performance is very good, to prevent aluminum in the cutting process Sticky knife phenomenon.
　　
For some of the surface finishing, we mainly use the processing performance is relatively excellent aluminum alloy milling cutter, the main advantage of this tool is more durable, can reduce the number of tool change, improve the efficiency.
　　
Optimization of Tool Path for Machining Program
　　
In the operation process of tire mold pattern NC programming, first of all, it is necessary to load the blank, define the object of process processing, design the tool, define the processing method and generate the corresponding processing program. Then, according to the content of the processing program, such as the specific parameters of the processing object, the guiding mode of the tool, the milling step distance, the spindle speed, the feed rate, the milling angle, the advance and retreat cutter points, the interference surface and the safety plane, etc., the generation method of the tool path is established. After zui, a program that can be recognized by the machine tool is generated through post-processing to realize the processing of products. In this process, the key points of the problem can be analyzed one by one to realize the optimization of the program, so as to achieve the purpose of raising the rate.

　　
We need to continuously optimize the tool path in the processing process, and we must do the following:
　　
Fading mode
　　
In the past, we usually used the screw feed in the programming, which is a waste of time. Through continuous attempts, we used the slope milling feed.
　　
It can be seen from Figure 8 that the tool always maintains continuous cutting, so that the time for processing each groove is greatly shortened and the processing efficiency is improved.
　　
Reduce the advance and retreat of the knife, try to maintain the continuous cutting of the tool
　　
It can be seen from Figure 9 that the tool always keeps continuous cutting, and there is only one feed and withdrawal process from the beginning to the end of the tool, which saves a lot of time and improves production efficiency.
　　
Minimize empty knife after knife path optimization
　　
(1) In the processing process, try to maintain a large and stable cutting speed, and give full play to the performance of machine tools and tools.
　　
(2) to avoid the discontinuous and sudden change of acceleration during processing, some arc transition sections can be added to the program section.
　　
(3) When the tool moves, maintain a constant spindle feed and produce the same volume of chips.
　　
(4) Reduce the change of milling load as much as possible to make the machining allowance control uniform.
　　
(5) reduce no cutting movement, no vertical direction of the beat, no drastic changes in the direction of cutting.
　　
(6) small cutting large feed rate, cutting, while improving tool life.
　　
(7) Under the premise of ensuring the interpolation tolerance, reduce the program length as much as possible.
　　
(8) Provide a highly continuous smooth path trajectory.
　　
CNC machine tools as a rate of equipment, to give full play to its high-performance, high-precision and high-automation characteristics, in addition to the must master the performance of the machine, characteristics and methods of operation, but also in the program before the detailed process analysis and determine the reasonable processing technology, in order to get the * processing program.
　　
In this paper, through the correct choice of cutting tools and the comparison of the optimization results of the processing tool path, we can know that the tire pattern mold in CNC machining must be for the particularity of its structure, complexity, variability and other characteristics, choose the right tool, while improving the processing tool route, in order to improve the processing efficiency, reflecting the efficiency and advantages of CNC machining.
　　
In fact, in the process of tire pattern mold processing, many other contents can be optimized to improve the rate, such as the adoption of programming software, the use of fast clamping and fast positioning of the fixture, etc.