General steps of plastic parts designPlastic parts are designed on the basis of industrial modeling. First, see whether there are similar products for reference, and then carry out detailed functional decomposition of products and parts to determine the main process problems such as parts folding, wall thickness, demoulding slope, transition treatment between parts, connection treatment and strength treatment of parts.1. Similar reference

Before design, first look for similar products of the company and peers, what problems and deficiencies have occurred in the original products, and refer to the existing mature structure to avoid problematic structural forms.2. Determine the part discount, transition, connection and clearance treatment between partsUnderstand the modeling style from the modeling drawing and effect drawing, cooperate with the functional decomposition of the product, determine the number of parts (different surface states are either divided into different parts, or there must be over treatment between different surfaces), determine the over treatment between parts' surfaces, and determine the connection mode and fit clearance between parts.

3. Determination of part strength and connection strengthDetermine the wall thickness of the part body according to the product size. The strength of the part itself is determined by the wall thickness of the plastic part, the structural form (the plastic part in the shape of a flat plate has the worst strength), the stiffener and the stiffener. While determining the single strength of parts, the connection strength between parts must be determined. The methods to change the connection strength include: adding screw column, adding stop, adding buckle position and adding reinforcing bone against top and bottom.4. Determination of demoulding slope

The demoulding slope shall be comprehensively determined according to the material (PP, PE silica gel and rubber can be demoulded forcibly), surface state (the slope of decorative grain shall be greater than that of smooth surface, and the slope of etched surface shall be 0.5 degrees greater than that required by the template as far as possible, so as to ensure that the etched surface will not be damaged and improve the yield of products), transparency or not determines the demoulding slope of parts (the transparent slope shall be greater).Material types recommended by different product series of the companySurface treatment of plastic parts

Wall thickness selection of plastic partsFor plastic parts, the uniformity of wall thickness is required, and the workpiece with uneven wall thickness will have shrinkage traces. It is required that the ratio of stiffener to main wall thickness should be less than 0.4, and the maximum ratio should not exceed 0.6.Demoulding slope of plastic parts

In the construction of stereoscopic drawing, where the appearance and assembly are affected, the slope needs to be drawn, and the slope is generally not drawn for stiffeners.The demoulding slope of plastic parts is determined by the material, surface decoration status and whether the parts are transparent or not. The demoulding slope of hard plastic is greater than that of soft plastic. The higher the part, the deeper the hole, and the smaller the slope.Recommended demoulding slope for different materials

Numerical values of different accuracy in different size rangesDimensional accuracy of plastic partsGenerally, the accuracy of plastic parts is not high. In practical use, we mainly check the assembly dimensions, and mainly mark the overall dimensions, assembly dimensions and other dimensions that need to be controlled on the plan.

In practice, we mainly consider the consistency of dimensions. The edges of the upper and lower covers need to be aligned.Economic accuracy of different materialsNumerical values of different accuracy in different size ranges

Surface roughness of plastics1) The roughness of the etched surface cannot be marked. Where the plastic surface finish is particularly high, circle this range and mark the surface state as mirror.2) The surface of plastic parts is generally smooth and bright, and the surface roughness is generally ra2.5 0.2um.

3) The surface roughness of plastic mainly depends on the surface roughness of mold cavity. The surface roughness of mold is required to be one to two levels higher than that of plastic parts. The mold surface can reach ra0.05 by ultrasonic and electrolytic polishing.FilletThe fillet value of injection molding is determined by the adjacent wall thickness, generally 0.5 1.5 times of the wall thickness, but not less than 0.5mm.

The position of the parting surface shall be carefully selected. There is a fillet on the parting surface, and the fillet part shall be on the other side of the die. It is difficult to make, and there are fine trace lines at the fillet. However, fillet is required when anti cutting hand is required.Stiffener problemThe injection molding process is similar to the casting process. The non-uniformity of wall thickness will produce shrinkage defects. Generally, the wall thickness of reinforcement is 0.4 times of the main body thickness, and the maximum is no more than 0.6 times. The spacing between bars is greater than 4T, and the height of bars is less than 3T. In the method of improving the strength of parts, it is generally reinforced without increasing the wall thickness.

The reinforcement of the screw column shall be at least 1.0mm lower than the end face of the column, and the reinforcement shall be at least 1.0mm lower than the part surface or the parting surface.When multiple bars intersect, pay attention to the non-uniformity of wall thickness caused by the intersection.Design of stiffeners for plastic parts

Bearing surfacePlastic is easy to deform. In terms of positioning, it should be classified as the positioning of wool embryo. In terms of positioning area, it should be small. For example, the support of plane should be changed into small convex points and convex rings.Oblique roof and row position

The inclined top and row position move in the parting direction and perpendicular to the parting direction. The inclined top and row position shall be perpendicular to the parting direction, and there shall be sufficient movement space, as shown in the following figure:Treatment of plastic limit process problems1) Special treatment of wall thickness

For particularly large workpieces, such as the shell of toy cars, the wall thickness can be relatively thin by using the method of multi-point glue feeding. The local glue position of the column is thick, which is treated as shown in the following figure.Special treatment of wall thickness2) Treatment of small slope and vertical surface

The die surface has high dimensional accuracy, high surface finish, small demoulding resistance and small demoulding slope. In order to achieve this purpose, the parts with small inclination of the workpiece are inserted separately, and the inserts are processed by wire cutting and grinding, as shown in the figure below.To ensure that the side wall is vertical, the running position or inclined top is required. There is an interface line at the running position. In order to avoid obvious interface, the wiring is generally placed at the junction of fillet and large surface.Treatment of small slope and vertical surface

To ensure that the side wall is vertical, the running position or inclined top is required. There is an interface line at the running position. In order to avoid obvious interface, the wiring is generally placed at the junction of fillet and large surface.Problems often to be solved for plastic parts1) Transition processing problem

The accuracy of plastic parts is generally not high. There must be transition treatment between adjacent parts and different surfaces of the same part.Small grooves are generally used for transition between different surfaces of the same part, and small grooves and high-low staggered surfaces can be used between different parts, as shown in the figure.Surface over treatment

2) Clearance value of plastic partsParts are directly assembled without movement, generally 0.1mm;The seam is generally 0.15mm;

The minimum clearance between parts without contact is 0.3mm, generally 0.5mm.3) The common forms and clearance of plastic parts are shown in the figureCommon forms and clearance taking method of stop of plastic parts

1. Fault phenomenonWhen changing the knife, the manipulator is stuck and cannot change the knife. The position of the manipulator for changing the knife is offset, and the knife is changed.2 fault analysis and treatment

2.1 tool change principleThe machining center is a rotary tool magazine, and the tool change mechanism is cam type. The tool change process is as follows:(1) Write m06t01 to start the tool change and tool selection cycle.

(2) The spindle will stop at the oriented spindle stop point, the coolant stops, and the z-axis moves to the tool change position (second reference point).(3) Select the tool. After NC compiles it to PLC according to the t command, start selecting the tool. The tool magazine motor rotates and rotates the target tool number to the tool change point of the tool magazine. Note that the t command is the tool sleeve position of the tool magazine at this time.(4) The tool change motor drives the cam mechanism to rotate 90 from the parking position to grasp the tool in the effective tool sleeve and the tool in the spindle. At the same time, detect the change of the proximity switch state of the cam mechanism, the PMC output sends out the tool loosening command, the tool magazine tool sleeve tool loosening and the spindle tool loosening solenoid valve are powered on, the cam continues to rotate, drive the manipulator down, push down the tool handle and prepare for exchange. As shown in Figure 1.

(5) The manipulator rotates 180 to exchange the tool, the cam continues to move upward, install the tool into the spindle, and install the tool on the original spindle into the tool sleeve at the tool change position of the tool magazine. At the same time, the detection switch sends a tool tightening command to PMC, the solenoid valve loses power, the shaft tool handle is clamped, the butterfly spring retracts, and the spindle tool is clamped.(6) Change to the manipulator, continue to rotate 90 , and stop completing a set of tool change actions.2.2 fault analysis

Change the tool to the fourth step of 2.1. The tool change manipulator is stuck, and the spindle has been loosened for blowing, but the tool cannot be pulled out. Cut off the power and manually turn the tool change motor. After completing a tool change action, manually load and unload the tool, the action is normal, and the problems of spindle tightening tool are preliminarily eliminated. When the tool change process is performed again, the manipulator gets stuck and the manipulator claw at the tool magazine falls off. After the tool change is found, the manipulator installs the tool on the spindle and the position is offset, as shown in Figure 2.

After the tool is removed, it is found that the action is normal. The reason for this situation may be the offset between the manipulator and the spindle, or the deviation of the accuracy of the manipulator axis relative to the spindle axis, and the inaccurate positioning of the spindle will also lead to the offset of the tool change position. Implement the tool change action step by step, check the accurate positioning of the spindle, and eliminate the fault caused by inaccurate positioning. According to the table, the mechanicalThe axial position and rotation center distance of hand, knife sleeve and spindle are consistent, so the fault of mechanical jamming of mechanical mobile phone is also eliminated.

Recently, this machine tool mainly processes stainless steel and other material workpieces, with large cutting volume and heavy load. It runs under re cutting for a long time. It is found that the manipulator is not loose and the telescopic action of the manipulator claw is flexible. However, it is found that the adjustment block on the manipulator is worn. It is disassembled and observed that the adjustment block is mainly used to clamp the tool handle. After re repair and processing, try again, The offset disappears at the spindle position. The main cause of this fault is the large impact of the manipulator and frequent tool change, resulting in the loosening and wear of the clamping claw, as shown in Figure 3.

Nowadays, smart phones have changed from plastic back cover to thin metal body. Although the smart appearance attracts consumers, the production process of mobile phone case parts suppliers is more difficult. Only because the cutting and processing of the case requires quite high precision, even if it is only a small deviation, it may cause workpiece scrapping and erode profits.

In order to improve the yield of CNC processing, mobile phone box manufacturers are often forced to change tools frequently to ensure that CNC machines maintain a normal production beat, but this leads to an increase in the cost of consumables and also affects profits. In addition, the mobile phone case processing industry attaches great importance to the production rate, for fear that the sudden failure of CNC cutting machine will lead to negative chain reactions such as production capacity decline and delivery delay, which will damage customer satisfaction and goodwill. Therefore, it allocates manpower to carry out regular inspection and entrusts outsourcers to provide second-line maintenance support, but these methods are passive, It is difficult to effectively deal with abnormal conditions at the first time.

Mobile phone case is one of the cases of CNC machine application. CNC cutting is widely used in various processing and manufacturing, and various suppliers are facing a similar profit defense war. Xu Changyi, manager of Linghua technology measurement and automation products division, believes that whether you want to improve the machining accuracy or increase the productivity, the axe bottom salary drawing plan is to monitor the cutting process, especially the vibration monitoring, mainly because once the vibration value of the machine rises beyond the reasonable range due to imbalance, resonance or misalignment, It is easy to affect the operation of the machine, resulting in fault shutdown.

PC based monitoring solution is better than PLC solution to capture fine vibration signals

If the CNC processing machine can be endowed with intelligence and built with a set of full-time vibration monitoring mechanism, it can diagnose the health state of the machine at any time. Instead of waiting for the output of the final finished product and judging the cause of the abnormality afterwards, it can detect the unusual state of the processing machine in real time through preventive detection in advance and take corresponding treatment measures quickly, Including optimizing and adjusting processing parameters (such as changing spindle speed), or changing tools, etc. to solve small deviations immediately and avoid causing major disasters in the future.

It can not be denied that the cutting vibration monitoring of CNC machining machines is not a new topic at this moment. In the past, there were some PLC solutions with the demand of simplicity and convenience, which boasted that as long as the CNC machine was connected, it could produce utility quickly; Therefore, it is inevitable that some people wonder why PC based monitoring scheme is needed since PLC is available to assist in cutting vibration monitoring?

The so-called devil lies in the details. Some subtle vibration signals or high-frequency signals reflect some facts to some extent. It may be that the connecting mechanism begins to be unbalanced, the rotating spindle bearing ball breaks and affects the transmission power, or the fasteners become loose, which means that the CNC machining machine begins to "get sick", and the symptoms are different with the different machine characteristics; These subtle and changeable signs are not easy to capture by virtue of the PLC solution with the characteristics of low sampling rate, supporting limited bandwidth range and fixed algorithm. If the CNC monitoring solution can capture small changes and help users quickly grasp the key factors that may lead to reduced accuracy or capacity decline, they can respond as soon as possible.

In view of this, Linghua launched a cutting vibration monitoring scheme called mcm-100, which boasts that it can carry out 24-hour continuous data acquisition and vibration measurement for rotating transfer machinery and equipment under the condition of high precision and high sampling rate, and integrate the functions of data collection, vibration analysis and calculation, operation, Internet access and so on, Assist CNC machine users to successfully solve various challenges faced by traditional cutting process, and endow CNC machine with intelligence in the most relaxed and burden-free way.Achieve the wonderful effect of preventive maintenance through high-precision monitoring

Xu Changyi explained that generally speaking, there are three detection situations that CNC machines most want to establish. One is "spindle vibration detection", which aims to monitor the vibration of the spindle during cutting. The method is to directly measure the RMS value of the time domain signal. If it exceeds the critical value, reduce the speed or stop running; The second is "bearing quality diagnostic tic", which is intended to diagnose the health status of bearings. It is carried out when CNC does not perform cutting and only idles at high speed; The third is "spindle collision detection", which is used to detect the spindle collision. When the vibration wave pattern meets some default conditions, it is judged that the collision has occurred, and the spindle movement is stopped immediately.

The above situations 1 and 2 are closely related to the accuracy and bandwidth range of vibration signals. PLC solutions can capture very little information, which is difficult to help users establish contingency strategies; In contrast, mcm-100 not only has 24 bit high resolution capability (generally falling in the range of 12 or 16 bit), but also can capture high-frequency signals with a sampling rate of up to 128ks / S (generally only supporting 20Ks / s or even lower), so as to provide users with more vibration analysis materials.New business opportunities for CNC machine equipment manufacturers

On the other hand, the cutting vibration monitoring scheme can also create new business opportunities for CNC machine equipment manufacturers. As CNC machine equipment suppliers are exposed to a large amount of vibration information, once combined with big data analysis, they have a more thorough understanding of the correlation between signal changes and machine failures. CNC machine equipment suppliers can make good use of the accumulated knowledge assets, give birth to value-added services, and even adjust their business model from selling out equipment to selling machine operation hours, Establish long-term stable income. According to Linghua technology, the operator of PC based cutting vibration monitoring scheme, the vibration monitoring scheme has entered the landing stage and has been adopted by various well-known CNC tool machine manufacturers, and its demand has increased significantly in 2017, which shows that both CNC processors and CNC tool machine manufacturers have increasingly keen demand for CNC cutting vibration monitoring scheme.