GB/T 39812-2021Plastics - Preparation of test specimens by machining (English PDF)

3.1 Milling

Note. In the milling process, the power of the tool includes a ring-shaped main motion and the appropriate feed motion of the workpiece. The rotation axis of the main motion is used to maintain the

The position of the machining tool is independent of the feed movement (see ISO 3855). The finished dumbbell specimens and rectangular specimens as well as the size of the notch are all available

To be prepared by milling.

3.1.1 Geometry (see ISO 3002-1 and Figure 1)

Note. This standard is only related to some details such as the precise geometric dimensions of the milling cutter in ISO 3002-1 and the given position of the corresponding tool of the workpiece.

3.1.1.1

Tool-cutting-edgeangel

alphar

The angle between the cutting edge plane Ps of the sample measured on the back plane Pr of the tool and the assumed working plane Pf.

3.1.1.2

Toolbackclearance

alphap

The angle between the tool side surface Aalpha and the tool cutting edge plane Ps measured in the tool back plane Pp.

3.1.1.3

Toolsideclearance

alphaf

The angle between the tool side surface Aalpha and the tool cutting edge plane Ps measured on the assumed working plane Pf.

3.5 Stamping of specimens of any shape made from thin plates

Note. In this method, under high pressure, a tool with a sharp edge of hard steel and parallel to the thin plate is used to punch a sample of any shape from the thin plate.

3.5.1 Geometry

3.5.1.1

Shapeofstampingtool

The punching edge of the punching tool is located on a plane parallel to the plate, and the shape of the punching edge depends on the shape of the sample to be prepared.

Shape, size and required tolerances.

3.5.2 Force and movement of tools

3.5.2.1

Contact force

Fc

The value of the force applied to the punching tool perpendicular to the plane of the sheet.

Note. The unit is Newton (N).

3.5.2.2

Feedspeed

vf

The instantaneous speed at which the cutting edge of the punching tool feeds perpendicular to the plane of the plate.

Note. The unit is meter per minute (m/min).

4.1 The shape and state of the sample

This standard describes the processing methods for the following types of specimens.

---Rectangular spline;

---Spline with notched rectangle;

---Rectangular plate;

---Curve sample (such as dumbbell);

---plate.

The precise shape, size and tolerance of the sample shall comply with the test method required by the standard. Observe with a low-power magnifying glass (approximately 5 times) to obtain

There should be no obvious cracks, scratches or other defects on the surface and edges of the sample.

The rectangular spline should not be distorted, and the opposite sides should be parallel to each other. The surface and edges are free of scratches, dents, defects and distortions. Each sample shall be in accordance with

These require visual observation and micrometer measurement to ensure that the edges are straight, rectangular, and the surface is flat.

The impact penetration test requires lower edge quality of the disc-shaped specimen than the tensile test.

Any sample that does not meet all the above requirements should not be used, or be processed to meet the conditions before use.

4.2 Sample preparation

The sample should be a plate or sheet made of semi-finished materials obtained from compression molding, injection molding, casting, in-situ polymerization, extrusion or other processing processes.

Obtained on processing. It is also possible to use suitable processing methods to obtain plates from the finished product. If the substrate used to prepare the sample is not uniform, the

The main axis of the specimen should be parallel or perpendicular to the main direction axis of the material. The exact conditions for preparing the sample, the location and direction of the sample in the sample should be determined by

The relevant party decides and records it in the test report.

Note. Room temperature and the temperature of the sample during processing may affect the properties of the sample.

5.1 Overview

The machines specified in 5.2~5.6 (see also Chapter 3) can be used to process plastic materials to obtain specimens and obtain the notches of the specimens. Do not

The properties of the same sample and the recommended processing conditions for the sample material are shown in Table 1.The processing conditions required for each material will be specified in the ISO standard of the corresponding material.

It is given in the specifications for sample preparation and performance measurement. Although the notch processing conditions given in Table 1 meet the processing requirements of multiple samples,

Due to the variety of test materials, there may still be other suitable processing conditions.

5.2 Milling cutter

A milling cutter can be used to prepare dumbbell and rectangular strip specimens. The milling cutter contains one tooth or a row of teeth specified in ISO 3855, and can be more

A milling cutter for cutting at a high speed (at high speeds, such as profile milling equipment). The milling cutter can also be used to machine notches on the rectangular strip specimens, in this case

Next, only when the quality of all the teeth are the same, can a milling cutter with more than one tooth be used.

5.3 Slicing or sawing machine

It can be used for the processing of rectangular strips or plate samples. Can be equipped with circular or band saw or edges should be coated with diamond or cubic boron nitride grinding

Material disc.

5.4 Tube cutting machine

Used for processing disk-shaped specimens from plate or sheet materials. The cutting edges should be serrated or coated with abrasives.

5.5 Lathe

Used for the same as described in 5.4, cut a disc sample from a single pre-formed sheet.

5.6 Planer

Used to cut finished products or slice rectangular strips and notches.

5.7 Punching tools

Used for stamping thin plates made of materials with sufficient ductility to make specimens of any shape.

5.8 Broaching tools

Used for processing gaps. Divided into manual or mechanical drive.

6.1 Overview

The processing speed is determined by the sample material, and overheating should be avoided, especially for thermoplastic materials. If necessary, use cooling medium, ISO material

The standard will be stated in the specifications for sample preparation and performance measurement. The cooling medium should not affect the processing of the sample (see also Table 1). Fine play

Grind the sample to obtain a smooth surface. For tools whose edges are covered with diamond, cubic boron nitride or other abrasives, please refer to ISO 21950, ISO 6104,

And ISO 6106.

When processing samples, be careful to avoid skin contact and inhalation of dust to avoid allergies.

6.2 Dumbbell sample preparation

Use manual low-speed milling or use high-speed profiling milling (preferred) according to the conditions in Table 1 to prepare specimens.

Use a magnifying glass (5 times magnification) to inspect the milled surface and edges of the sample to observe whether there are cracks, scratches, and other defects. cut

After cutting 500 samples, use a microscope or projector (50 times to 100 times magnification) to check the cutting edge of the tool.

6.3 Prepare rectangular specimens by sawing or cutting with a grinding disc

The detailed conditions are shown in Table 1.Only when there are no special requirements for the surface quality of the sample, or the surface of the sample will be milled or planed later

When the method is processed, the sample is prepared by sawing. In the latter case, check the surface of the sample as required in 6.2.

6.4 Preparation of disk-shaped specimens

Generally, disk-shaped specimens are used for impact penetration tests. In this case, the defects of the machined surface will not seriously affect the test results. use

Prepare the sample under the conditions given in Table 1, and ensure that the surface of the sample is smooth and flawless.

6.5 Punching sampling of samples of any shape

Only when the sample material is sufficiently soft and the sample is a sufficiently thin sheet, use this method to prepare the sample. Use a knife with a sharp

The blade, a punching machine with appropriate shape and size, punches the sample from the test plate at one time. The cutting edge of the punch should be sharp enough without notches.

The test panel should be placed on a smooth, slightly soft surface (such as leather, rubber or better quality cardboard), and a flat, hard surface should be placed on the lower layer of the surface.

质材料。 Quality materials.

The method specified in this standard is applicable to the preparation of the sample edge and surface that meet the requirements of 6.2.

6.6 Preparation of specimen notches by milling or broaching

Use a milling or broaching machine or lathe to cut the specimen, preferably a single-tooth cutting machine. Use cutting edges of high-speed steel, hard steel or diamond

Stone tools. Only when the quality of all the cut notches is the same as that cut by a single-tooth cutter, can the milling cutter with multi-tooth be used. Stamping

The sample obtained needs to be notched through secondary processing (that is, notches cannot be stamped).

When processing the incision, no abrasive (embroid) is allowed.

When milling, select the feed speed so that the cutting thickness ds is between 0.003mm and 0.07mm (see Figure 2 and Figure 3). Thickness ds

(mm) is given by formula (1).

ds=vf2/(n2.R) (1)

Where.

vf---feed speed, the unit is millimeters per minute (mm/min);

n --- Tool rotation speed, the unit is revolutions per minute (r/min);

R ---The distance between the milling machine and the tool tip, in millimeters (mm).

The contour and radius of the incision are the key to establishing close tolerances, because these parameters will significantly affect the degree of stress concentration at the bottom of the incision. for

To obtain reproducible results, the cutting edges need to be carefully polished to ensure that they are sharp and free of scratches and burrs.

Before using the cutting tool, or after cutting about 500 incisions, or after cutting hard and wear-resistant materials, check the sharpness of the tool.

There are cracks, accurate tip radius and contour. If the radius and contour exceed the specified range, replace with a new sharp and burr-free tool.

Use a microscope or projector with a magnification of 50 to 100 times to check the tool and the gap. For single-tooth tools, if the tool tip

The contour corresponds to the contour of the specimen cut or there is a definite relationship between the two. The contour of the tool tip can be checked instead of the contour of the specimen notch.

an examination. Facts have proved that the same tool cuts different materials, and the contour of the notch may be different.

For transparent materials, the photoelastic effect can often be used to check for undesirable changes in the sample. For example, undesirable caused by processing

Heating or melting, so that there are clearly visible colored interface lines or surfaces in the area near the processed surface, especially for injection molded samples.

The test experience of notched specimens shows that even if the visually meeting the requirements of the tool is selected, the gap of some materials (such as PMMA, PC)

The sample test results are still gradually decreasing. In these cases, it is recommended to use the reference material to check the tool.