April 2021 – Page 6 – CNC Machining & Turning, Milling, Metal parts

How to make precision parts

Numerical control tool is one of the preconditions to improve machining efficiency, its selection depends on the geometry of the machined parts, material state, fixture and machine tool rigidity. The following aspects should be considered:

(1) The cutting tool is selected according to the cutting performance of the part material. For example, turning or milling high strength steel, titanium alloy and stainless steel parts, it is recommended to choose indexable carbide tools with good wear resistance.

(2) The tool is selected according to the processing stage of hardware parts. That is to say, the roughing stage is mainly to remove the allowance, and the tool with better rigidity and lower accuracy should be selected. The semi finishing and finishing stages are mainly to ensure the machining accuracy and product quality of the parts, and the tool with high durability and high accuracy should be selected. The precision of the tool used in the roughing stage is the lowest, while the precision of the tool used in the finishing stage is the highest. If the same tool is selected for rough machining and finish machining, it is suggested that the tool eliminated from finish machining should be selected for rough machining, because the wear of tool eliminated from finish machining is mostly slight edge wear, and the coating is worn and polished. Continued use will affect the machining quality of finish machining, but has less impact on rough machining.

(3) According to the characteristics of NC lathe processing area, the tool and geometric parameters are selected. If the structure of the part permits, the cutter with large diameter and small ratio of length to diameter should be selected; the end edge of the over center milling cutter for cutting thin and ultra-thin wall parts should have enough centripetal angle to reduce the cutting force of the cutter and cutting parts. When machining soft material parts such as aluminum and copper, the end mill with slightly larger rake angle should be selected, and the number of teeth should not exceed 4.

When selecting the cutting tool, the size of the cutting tool should be adapted to the surface size of the workpiece. In production, end milling cutter is often used to process the peripheral contour of plane parts; when milling plane, cemented carbide blade milling cutter should be selected; when machining boss and groove, high speed steel end milling cutter should be selected; when machining rough surface or rough hole, corn milling cutter with cemented carbide blade can be selected; Ball end milling cutter, ring milling cutter, cone milling cutter and disk milling cutter are often used to process some solid surface and variable angle profile.

In free-form surface machining, because the end cutting speed of ball end cutter is zero, in order to ensure the NC machining accuracy, the cutting line spacing is generally very small, so ball end milling cutter is suitable for surface finishing. The end milling cutter is much better than the ball end milling cutter both in the surface processing quality and processing efficiency. Therefore, on the premise of ensuring that the parts can not be cut, the end milling cutter should be selected as far as possible when rough machining and semi finish machining curved surface.

In the machining center, all the tools are pre installed in the tool library, and the corresponding tool change action is carried out through the tool selection and tool change instructions of the NC program.

Computer gong processing surface treatment:

In terms of appearance, the machined surface of the parts shall not have obvious defects such as scratches and scratches.
The surface of products processed by CNC lathe must be smooth, beautiful, no burr, no flash, etc
In terms of quality, the machined surface of parts must meet the requirements of corrosion resistance, wear resistance and hardness.

In order to meet the accuracy of parts processing, it must also meet the surface technical requirements and appearance requirements. The parts we process can’t appear to be full of burrs. Here we introduce the surface processing requirements of CNC lathe

In terms of appearance, the machined surface of the parts shall not have obvious defects such as scratches and scratches.
The surface of products processed by CNC lathe must be smooth, beautiful, no burr, no flash, etc
In terms of quality, the machined surface of parts must meet the requirements of corrosion resistance, wear resistance and hardness.
Selection principle of cutting parameters

According to the cutting requirements, first determine the back cutting amount AP, then look up the table to get the feed, and then look up the table to calculate the main cutting speed u through the formula.

In many cases, we can use empirical data to determine the value of these three elements.

Selection method of cutting parameters

Practice has proved that the selection of reasonable cutting parameters is related to many factors such as machine tool, cutting tool, workpiece and technology. The method of reasonable selection of processing amount is as follows:

In rough machining, it is necessary to ensure high production efficiency, so it is necessary to choose a larger back draft a. , larger feed rate,, low cutting speed u is selected.

When finishing, it is mainly to ensure the size and surface accuracy of the parts, so it is necessary to select smaller back feed AP, smaller feed, and higher cutting speed U.

In rough machining, it is necessary to give full play to the potential of NC lathe and the cutting ability of cutting tools. In the semi finish machining and finish machining of CNC lathe factory, how to ensure the machining quality should be considered, and on this basis, the productivity should be improved as much as possible. When selecting the cutting parameters, the CNC lathe factory should ensure that the cutting tool can complete a part or ensure that the durability of the cutting tool is not less than one working shift, at least not less than half a working shift. The specific value of CNC lathe factory should be selected according to the provisions in the machine tool manual, tool durability and practical experience.

(1) It’s a choice to take a knife on your back. The selection of back cutting amount should be determined according to the rigidity of machine tool, fixture, fixture and workpiece as well as the power of machine tool. In the case of the process system allows, as far as possible to choose a larger amount of back knife. In addition to the allowance left for the subsequent process, the rest of the rough machining allowance should be cut off as far as possible to minimize the number of tool runs.

Generally, on medium power machine tools, the back draft of rough machining is 8-10 mm (one side). The back feed of CNC lathe factory is 0.5-5 mm for semi finishing and 0.2-1.5 mm for finishing.

(2) The feed rate is determined. Feed rate refers to the change of tool feed direction in unit time. Numerical control lathe factory moving distance. The principle of determining the feed rate is: when the quality requirements of the workpiece can be guaranteed, in order to improve the productivity, a higher feed rate can be selected. When cutting, turning deep hole or finishing lathe, the CNC lathe factory should choose a lower feed speed. The feed speed should be adapted to the spindle speed and back feed.

Notes for computer gong processing:

Confirm the model, size and machining allowance of the blank according to the program sheet before operation, and remove sand and polish the blank
After operation, confirm the position of the workpiece and the processing sequence, and complete the table comparison
In the process of centring, if the “centring rod” is needed, the rotating speed is 501r / m. if the cutter is used, the rotating speed depends on the cutter. In this process, the data must be taken at the same height to ensure the accuracy of centring. After centring, the “G0 g54 x0 Y0” can be used for inspection
Before formal processing, check and confirm the position of the workpiece and whether the data is correct

Precautions during processing:

Before processing each program, it is necessary to strictly confirm whether the tool is consistent with the program
When loading the tool, it is necessary to confirm whether the length of the tool and the selected tool holder are suitable
In the same workpiece, each tool setting should be kept in the same area to ensure the accuracy of tool receiving
Try to blow with air in roughing procedure and spray oil in smooth knife procedure
Clean up the aluminum slag in the machine tool before light knife oil injection to prevent the aluminum slag from absorbing oil
During the self operation of the machine tool, the operator is not allowed to leave the machine tool or check the operation status of the machine tool regularly. If he / she needs to leave midway, he / she must appoint relevant personnel to check
If excessive machining allowance is found in the process of machining, it is necessary to use “single section” or “pause” to clear x, y and Z values, then mill them manually, and then swing them back to “zero” to let them run by themselves
In case of tool collision during machining, the operator must stop the machine immediately, such as pressing the “emergency stop” button or “reset” button or setting the “feed rate” to zero
Do not open the door when the machine tool is running to avoid flying knife or workpiece
The workpiece must be cleaned and deburred in time
At the end of work, the operator must make timely and accurate handover to ensure the normal follow-up processing
Before turning off the machine, make sure that the tool magazine is in the original position and the XYZ axis stops in the middle position. Turn off the power supply and the main power supply on the operation panel of the machine in turn

Computer gong processing with multi axis

Fully enclosed protection. All CNC computer gongs have protective doors. When processing, closing the protective doors can effectively prevent personal injury accidents.
The CNC computer gong generally has multiple feed axes (more than three axes) and even multiple spindles, and the number of linkage axes is also very large, such as three-axis linkage, five axis linkage, seven axis linkage and so on. Therefore, it can actively complete the processing of multiple planes and multiple viewpoints, and finish the high-precision processing of messy parts. The CNC computer gong can finish milling, boring, drilling, expanding, reaming, tapping and other processing with high concentration.
The CNC computer gong is equipped with a tool magazine and an active tool changing device. Before processing, the required tools are loaded into the tool magazine, and the tools can be replaced actively through program control.
The use of multiple worktables, worktable active exchange CNC computer gong processing, if with active exchange worktable, can end a worktable in the processing together, another worktable finish workpiece clamping, and then greatly shorten the auxiliary time, improve the processing power.
CNC computer gongs can be used for turning and grinding. For example, the circular worktable can drive the workpiece to rotate at high speed, and the cutting tool only makes the main motion without feeding. This makes CNC computer gongs have a wider processing scale
CNC computer gongs with high initiative, high precision and high power have high spindle speed, feed speed and rapid positioning accuracy. Through reasonable selection of cutting parameters, they can fully show the cutting performance of cutting tools and reduce cutting time. All kinds of auxiliary actions are fast and active, which reduces auxiliary action time and downtime. Therefore, CNC computer gongs are very popular The production power is very high.
High investment due to the high degree of intelligence, disordered structure and powerful function of CNC computer gong, the one-time investment and maintenance cost of CNC computer gong is much higher than that of ordinary machine tools.
In the appropriate conditions, the ability to perform the best benefits, that is, in the process of using the performance of the advantages of CNC machine tools, ability to fully reflect the benefits, which is very important for the rational use of CNC computer gongs.