A special marking method is introduced in this post, which “borrows materials” for blank defects, learns from each other’s strengths to make up for their weaknesses, and redistributes the allowance of the surface to be machined;
Avoid the heavy and take the light, and give priority to ensuring the key dimensions, which are used to remedy the unqualified blank and reduce the loss.
Due to mechanical operation, sometimes the contour of the blank is skewed or the hole is offset, so that the shape and size of the blank exceed the technical scope and become unqualified products.
If the offset and skew are not large, the allowance of each surface to be machined can be redistributed through scribing, so that the unqualified blank can be remedied.
This method of using scribing to remedy the blank is called “borrowing”.
Here are two factory examples to illustrate what “borrow” is and how to “borrow”.
2. Give consideration to the outer circle and inner hole and redistribute the blank allowance
Fig. 1 shows a disc-shaped casting part, with its inner hole concentric with the outer circle.
Fig. 1 disc casting parts
The normal blank is shown in Fig. 2, and the inner hole and the outer circle are basically not eccentric.
Fig. 2 normal blank
However, sometimes there is eccentricity between the inner hole and the outer circle of the cast blank due to casting errors.
Fig. 3 shows the eccentric blank with the eccentricity of 8mm.
Fig. 3 eccentric blank
Due to the 8mm eccentricity between the inner hole and the outer circle of the blank, if the inner hole center O1 of the blank is selected as the marking reference (see Fig. 4).
Fig. 4 takes the inner hole center O1 of the blank as the marking reference
Although the machining allowance of the inner hole is no problem, the machining allowance of the outer circle is not enough, and the most serious part is the lack of 3mm machining allowance;
If the outer circle center O2 of the blank is selected as the marking reference (see Fig. 5), although the machining allowance of the outer circle is no problem, the machining allowance of the inner hole is not enough, and the most serious part is the lack of 3mm machining allowance.
Fig. 5 takes the outer circle center O2 of the blank as the marking reference
Obviously, the inner hole or outer circle cannot be used as the marking benchmark.
At this time, the method of “borrowing materials” should be used to mark out.
The borrowing line is shown in Fig. 6.
Fig. 6 borrowing line
The specific method is to select the midpoint of the connecting line between the inner hole center O1 and the outer circle center O2 as the line reference.
Because of this scribing, the inner hole and outer circle have sufficient machining allowance, the inner hole has 1mm machining allowance at least, and the outer circle has 1mm machining allowance at least, so this scribing is feasible.
It avoids the scrap of blank and recovers the economic loss.
3. Give priority to ensuring the blank allowance of key parts
The normal blank of the part to be processed shown in Fig. 7 is shown in Fig. 8, with 5mm allowance on one side.
However, due to the error in casting, a piece is missing in the lower right corner of the blank, and the defective blank is shown in Fig. 9.
Fig. 7 parts to be processed
Fig. 8 normal blank
Fig. 9 defective blank
Since the length of the notch in the lower right corner in the horizontal and vertical directions is 25mm respectively, and the total allowance of the whole blank in the horizontal and vertical directions is 10mm respectively, it is obviously impossible to process this part in strict accordance with the drawing.
After communicating with the customer, it is learned that the part is used for the support of the bearing seat.
Even if there is a small gap in the lower right corner (as long as the side length does not exceed 12mm), it will not seriously affect its normal function.
Therefore, with the consent of the customer, the following measures are taken: the benchmark of the scribing was originally the center O of the square.
Now move it up and left by 3mm respectively to O1 point.
That is, the O1 point is used as the marking benchmark (see Fig. 10).
Fig. 10 take the O1 point as the marking reference
In this way, the left and upper edges of the part still have 2mm allowance respectively, and the lower and right edges have 8mm allowance respectively, and the allowance of semicircular groove is also sufficient at this time.
Although the notch in the lower right corner can not be avoided completely, the length of the remaining notch in the horizontal and vertical directions after processing is only 9mm respectively, so it will not seriously affect its use function, and the loss is recovered by borrowing materials.
In a machining plant, the person who specializes in marking is called line scriber.
It is generally held by experienced old employees.
It can be seen from the above cases that the line scriber has played a great role in ensuring product quality and saving cost, and should be paid enough attention.