The CNC machining industry needs to solve problems such as cutting technology, tool wear, machine tool accuracy and material changes. Technicians should summarize experience, learn new technologies, data analysis and optimization, and teamwork to improve production efficiency and product quality and promote industry development. When faced with common problems in the machining industry, technicians need a systematic approach to solve these challenges and ensure continuous improvement in production efficiency and quality. This article is a summary of common problems and solutions by CNC machinists and engineers from Xtmade.
General CNC machining sequence
In the CNC machining industry, the operation sequence is very important. It is related to the quality assurance of the product. If one sequence is wrong, it is easy to cause great losses. In serious cases, the parts need to be reprocessed, and the products processed first will be scrapped. Precision machining is one of them. So what is its sequence?
- The arrangement of precision machining sequence should be based on the structure of the parts and the condition of the blank, as well as the need for positioning and clamping. The key is that the rigidity of the workpiece is not destroyed.
(1) The processing of the previous process cannot affect the positioning and clamping of the next process. If there are general precision machining processes in the middle, they should also be considered comprehensively.
(2) The inner shape and inner cavity processing process should be carried out first, and then the outer shape processing process should be carried out.
(3) The processes with the same positioning, clamping method or the same tool are preferably connected to reduce the number of repeated positioning, tool changes and platen movements.
(4) For multiple processes carried out in the same installation, the process that causes less damage to the rigidity of the workpiece should be arranged first. Precision parts processing
- the centralized tool sorting method is to divide the process according to the tools used, and use the same tool to process all the parts that can be completed on the parts. Then use the second and third tools to complete the other parts that they can complete. This can reduce the number of tool changes, compress idle time, and reduce unnecessary positioning errors.
- the sorting method based on the processing parts For parts with a lot of processing content, the processing parts can be divided into several parts according to their structural characteristics, such as internal shape, external shape, curved surface or plane. Generally, the plane and positioning surface are processed first, and then the hole; simple geometric shapes are processed first, and then complex geometric shapes; parts with lower precision are processed first, and then parts with higher precision requirements. The above is the order of precision parts processing. You must follow these steps to operate, which will greatly reduce your processing risks.
Technical requirements for precision CNC machining
If you want to process precision parts, you need to be familiar with the relevant technical requirements to produce mechanical parts that meet the requirements. So what are the technical requirements for precision machining of mechanical parts? The following are the relevant issues and requirements we have summarized.
Contour processing of parts
- The shape tolerance of unmarked parts shall comply with the requirements of GB1184-80.
- The allowable deviation of unmarked length dimensions is ±0.5mm.
- The radius of unmarked fillets is R5.
- All unmarked chamfers are C2.
- Sharp corners are blunted.
- Sharp edges are blunted to remove burrs and flash.
Part surface treatment
- There should be no scratches, abrasions or other defects that damage the surface of the parts on the processed surface.
- The processed thread surface is not allowed to have defects such as black skin, bumps, random buckles and burrs. All steel parts that need to be painted must be free of rust, scale, grease, dust, dirt, salt and dirt before painting.
- Before rust removal, use organic solvents, alkali solution, emulsifier, steam, etc. to remove grease and dirt on the surface of steel parts.
- The time interval between the surface to be painted after shot blasting or manual rust removal and the primer should not be more than 6 hours.
- The surfaces of the riveted parts that are in contact with each other must be coated with anti-rust paint with a thickness of 30 to 40μm before connection. The overlapping edges should be sealed with paint, putty or adhesive. Primer damaged by processing or welding should be repainted.
Heat treatment of parts
- After quenching and tempering, HRC50~55.
- Medium carbon steel: 45 or 40Cr parts are subjected to high-frequency quenching, tempered at 350~370℃, HRC40~45.
- Carburizing depth 0.3mm.
- High temperature aging treatment.
Technical requirements for precision machining
- After finishing, the parts must not be placed directly on the ground, and necessary support and protection measures should be taken.
- The machined surface is not allowed to have rust and defects such as bumps and scratches that affect performance, life or appearance.
- The surface of the rolling finishing process must not peel after rolling.
- After the final process heat treatment, the surface of the parts should not have oxide scale. The mating surface and tooth surface after finishing should not have annealing
Sealing treatment of parts
- Each seal must be soaked in oil before assembly.
- Strictly check and remove the sharp corners, burrs and foreign matter left during part processing before assembly. Ensure that the seal is not scratched when installed.
- After bonding, remove the excess adhesive that has flowed out.
Gear technical requirements
- After the gear is assembled, the contact spots and side clearance of the tooth surface should comply with the provisions of GB10095 and GB11365.
- The reference end face of the gear (worm gear) should fit the shaft shoulder (or the end face of the positioning sleeve), and a 0.05mm feeler gauge should be used to check that it does not penetrate. The verticality requirements of the reference end face of the gear and the axis should be ensured.
- The joint surface of the gear box and the cover should have good contact.
CNC machining process specification
For CNC machining process specification, technicians determine the process to be adopted according to the product quantity, equipment conditions and worker quality, and write the relevant content into a process document, which is called a process specification. In order to facilitate the preparation, execution and production organization management of the process specification, the process needs to be divided into units at different levels. They are process, installation, station, work step and tool path. Among them, the process is the basic unit in the process. The machining process of parts consists of several processes. The following is a complete CNC machining process flow description summarized by the Xtmade team.
Process
The part of the process that a worker (or a group of workers) continuously completes on one (or several) workpieces at one workstation (or one machine tool) is called a process. The basis for dividing processes is whether the workstation changes and whether the work process is continuous.
For example: when processing a batch of shafts on a lathe, each shaft can be rough-machined and finished continuously, or the whole batch of shafts can be rough-machined first and then finished in sequence.
In the first case, the processing includes only one process; in the second case, due to the interruption of the continuity of the processing process, although the processing is carried out on the same machine tool, it becomes two processes. The process is the basic unit of the process and the basic unit of the production plan.
Installation
In the machining process, the process of clamping the workpiece in a correct position on the machine tool or in the fixture is called clamping. Sometimes, the workpiece needs to be clamped multiple times on the machine tool to complete the work content of a process. Installation refers to the part of the process content completed after the workpiece is clamped once.
For example, when machining a shaft on a lathe, first machine part of the surface from one end, then turn around and machine the other end. At this time, the process content includes two installations.
Workstation
When using a transfer (or shift) fixture, a rotary table or a multi-axis machine tool for processing, the workpiece is clamped on the machine tool once and then processed in several positions in sequence. The part of the process completed at each position occupied by the workpiece on the machine tool is called a workstation
In simple terms, the part of the process completed when the workpiece occupies a processing position relative to the machine tool or tool is called a workstation.
Work step
Under the condition that the machining surface, cutting tool, cutting speed and feed rate remain unchanged, the part of the process that is completed continuously is called a work step. It is also often called “feed” in production.
In order to improve productivity, the work step of using several tools to process several machining surfaces at the same time is called a compound work step, which can also be regarded as one work step.
Tool pass
The part of the process completed by the machining tool on the machining surface is called a tool pass.
For example, if the metal layer to be cut off of a shaft part is very thick, it needs to be cut several times. In this case, each cutting is called a tool pass. Therefore, under the premise of unchanged cutting speed and feed rate, the tool completes a feed movement called a tool pass.
Summary
Due to the complexity of CNC machining (such as different machine tools, different materials, different tools, different cutting methods, different parameter settings, etc.), it takes a long time to reach a certain level from engaging in CNC machining (whether machining or programming). This article is a summary of the knowledge and experience of CNC machining technology, procedures, etc. summarized by the xtmade engineers and machinists team in the long-term actual production process, which can be used for your reference.
Working with Xtmade
The above is the relevant processing skills knowledge points summarized by Xtmade’s team of engineers and machinists. If you need CNC machining, our team of experts can talk you through your part design drawings and help you choose the process that best suits your project. As a trusted CNC machining partner, Xtmade also provides high-quality CNC machining capabilities through CNC machining equipment based on routers, lathes, drills, and milling machines. Contact us today to get started. Visit our resource center to learn more about CNC machining, including tips for reducing costs and design best practices.
