Vacuum Forming Quality Control
Before writing the Vacuum Forming Quality Control steps, please allow me to do a simple introduction about vacuum forming processes, there are mainly five steps:
- Extrusion plastic sheets
- CNC aluminum molds
- Vacuum Forming
- CNC plastic
- After-treatment process (including assembly, painting, prototyping, and polishing)
Extrusion Plastic Sheets
Extrusion plastic sheets is a process of heating and melting plastic particles, then through the roll mold squeezing into different thickness and different surface appearance sheets. The sheets’ thickness can be 1-12mm, the width can reach 2000mm, the color can be any Pantone color, and we can also integrate different functions in the material.
Quality Control For For Thickness And Width
To control the thickness and width, we mainly adjusted the distance between the three roll molds to match the required sheet thickness. At the beginning of production, we will measure the accuracy between the roll molds. After extruding 20 meters in the length of the sheet, we also use calipers to measure the same plane of the sheet to avoid uneven conditions due to the material stacked. Also each extrusion of 20 meters in length, we will measure the distance between all the roll molds. The width is also checked like the same way.
Quality Control For Color
One of the most important tools to detect color is the colorimeter. We are able to produce all the colors on the Pantone color cards, and in the process of producing the sheets, we will use the results of the colorimeter to compare the Pantone color cards to measure whether the color of the sheets produced is within the error range. Another important point is How to ensure that the color of the product is consistent from batch to batch? There may be some places where the color of each batch of sheets is different or even the front and the back sections of the same batch of sheets are different. We will always control the color of the material with the following three points:
Firstly, Ditaiplastic has two large extrusion plastic sheets machines, and our sheet-making manager with over 20 years of experience, all sheet colors are mixed by ourselves, we make sure the color powder and the raw material particles are mixed well enough before extrusion. Secondly, to ensure that the color of different parts of the same batch of sheets is consistent, we will use a colorimeter to compare every 20 meters after the sheets are extruded. Last but not least, the recipe of each batch, which is the ratio of color powder to raw material, the mixing time, and the heating temperature will be recorded in the computer according to the customer’s name and the production date, and we will also cut a part of each batch after production to keep the sample. After the customer places an order, we also use a colorimeter to compare the two batches of sheets during production to ensure that the color error is within the range.
Quality Control For Different Functions
We can customize it by melting different characteristic particles, like fire-resistant, high-impact, cold-resistance, anti-corrosion, etc. For instance, to test the fire-resistant of the sheet, we will cut a part of the sheet into the vertical horizontal combustion test machine to do the test, the machine is mainly used to determine the non-combustibility of plastics under the direct combustion of the prescribed fire source, the test method is based on GB/T 2408 standard and UL and other standards to determine the fire resistance level of flame resistance materials, or will also directly use a lighter to test whether it can be lit. To test the high impact of the plastic sheet will use a professional impact test machine, through the program set each time the pendulum using the number of kilograms. Or just impact with a digger. For other characteristics, we will also use the machine to do professional testing.
Aluminum Mold/Aluminum Mould
For the molds used for vacuum forming, they can be roughly divided into four types: Casting aluminum is usually used for solid color and texture surface material, because casting aluminum mold is cheaper, and for the products with solid color or textured surface, the effect of casting aluminum molds can achieve the same effect of block aluminum molds. Block aluminum molds are often used for transparent products and products with a height of less than 100mm. Therefore, you can choose the type of mold according to your own requirements.
Texture acid-etched mold: Vacuum forming is a process of making a flat sheet into a 3D product, so it is indispensable to stretch the sheet to some extent. Usually, our textures are on the surface of the sheet, after vacuum forming, these sheets will also have a certain degree of stretching. The texture of the texture acid-etched mold is on the surface of the mold, which allows the material to have a very uniform texture distribution after the vacuum forming. The texture acid-etched molds are available in international standard color codes, and we are able to provide all color codes.
Sliding block mold: This kind of mold is usually applied to some products with under-cut structure, and the sliding of the module can better control the molding and demolding of the product. Once we received your 3D files or your samples, our engineer will analyze the design to check if it is suitable for the vacuum forming process and provide professional suggestions based on our experience. After all details of the drawing are confirmed, our engineer will convert the drawings into mold drawings according to the different shrinkage rates of different rates of different materials, which also means that the material must be selected before making the molds. After CNC is finished, we will polish and drill vacuum holes in the mold.
As we know, to make perfect plastic products, one of the necessary conditions is having a perfect mold, we have our own CNC mold machines, which can control the quality, price, and delivery date. And we will remark the mold for free if it is damaged or something bad happens to the mold, we will provide the best service if you have any needs.
How Do We Control The Mold's Quality
The manufacturing of the mold is actually done by adjusting the shrinkage rates of the 3D drawing as the first step. And there are four steps to verify the dimensions of a mold: First, use the finished mold to make samples on the vacuum forming machine, and verify the accuracy of the mold by measuring the sample dimension. Second, after completing the mold, the mold is scanned to obtain new 3D drawings of the completed mold and then compared to the original drawing after adjusting the shrinkage rates. However, the cost of using this test method can be very high. Third, compare the more important parts of the 3D drawing, we will make the fixture according to the size of these parts, and then compare it with the finished mold to see if it can match. For instance, for the back cover of the TV display where some parts need to be glued, and lock the screws, then there parts are important, we will use CNC carving a fixture for these places to stuck on the mold. The last one is, we will control the surface quality of the mold by polishing and drilling vacuum holes, neatly arranged drilling holes are especially important for texture acid-etched molds.
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Vacuum Forming
It should not be overlooked that the control of temperature is crucial for the vacuum forming process. And what is vacuum forming? Vacuum forming is one of the most common plastic processing processes. Simply saying, vacuum forming is a process that can make a flat sheet into a 3D shape product. While vacuum forming, may need two materials, one is the hot melt of the raw material particles and the extruded sheet, the other is the mold. The first half of this page is more detailed descriptions. Install the mold into a vacuum forming machine, raise up the mold, make the mold attached to the melting sheet 100%, and finally cool the product, and release the mold, we can get a wonderful product. About the vacuum forming quality control, let’s break it down into three sections:
Quality Control Of The Vacuum Forming Temperature
As mentioned above, temperature control is crucial for vacuum forming. In fact, there are two heating plates inside the vacuum forming machine, and each heating plate is divided into many heating zones. For different materials, different thicknesses of materials, and various shapes of products resulting in stretching in vacuum forming, the temperature needs to be precise for each heating zone. For each machine, for each product, we record the heating zone and the temperature of the heating zone. This can also ensure that the effect of vacuum forming is almost the same for different batches of products. We do not rely solely on human experience, but more on data. It is worth mentioning that our vacuum forming department manager has over 30 years of experience in the vacuum forming field.
Quality Control Of The Vacuum Forming Product's Thickness
Vacuum forming is actually essentially a material stretching cooling molding process, inevitably there will be material stretching, to detect the thickness of various parts, after forming is obviously not suitable for caliper measurement, this time we will use ultrasonic to measure the thickness of each part, to avoid the material after stretching too thin to produce bad effects, timely adjustment of the temperature of vacuum forming. In addition, we also increase the area and thickness of the material under the premise of ensuring the quality of product, the same product, the use of different thicknesses of material or the use of a larger area of raw material can vary greatly after vacuum forming.
Quality Control Of The Vacuum Forming Product Shape
In addition to the influence of the temperature on the shape, the subsequent practice after vacuum forming is also very important to the shape of the product. For instance, for some products made of PP or PE material, it usually takes longer to cool down after vacuum forming, and it is easy to shrink excessively after moving away from the vacuum forming machine which has the cooling system above the heating area, so it is necessary to make a fixture to fix the four edges of the product after vacuum forming to ensure better shaping. And when the product vacuum forming is completed, we will stack the product vertically on its side to prevent the deformation of the product due to incomplete cooling of the material, which is usually very sensitive to temperature.
CNC Cutting
CNC (Computer Numerical Control) is the further processing of the product after vacuum forming, which use to remove excess material from the outside of the product to obtain the required size and shape, drill and leveling of the product are all done by this step. We have two types of CNC cutting machines, one is five-axis and the other is three-axis, to total number is 28, and 16 sets of them are five-axis cutting machines, they can process 360 degrees in all directions and is fast and accurate, and they are suitable for complex structures, angles, and curved surfaces. So we can say that we are one of the largest CNC production departments in China. Usually, our CNC engineers type in the program, and the machine will automatically operate to cut the shape of the product.
Quality Control For The CNC Finished Part
To maintain the accuracy of cutting product: Take the five-axis cutting machines as an example, when we use the five-axis CNC processing cutting products before, we will make a fiberglass mold or wooden mold, and the surface shape of this mold will fit with the shape of the product, and the same time this mold we will drill holes and will embed one side of magnets on the surface of the mold, during the cutting process, the vacuum pump will extract the air between the mold and the product through the air holes on the top of the mold, the magnet will be placed of the surface of the product. Through the suction between the magnets and the suction of the vacuum pump, the product will be firmly attached to the mold, which is used to ensure that the size of the product is cut accurately.
