The correct use of coordinate measurement in mold acceptance

The correct use of coordinate measurement in mold acceptance
The key to three coordinate acceptance is not to measure too much, but to select the right measuring points: key dimensions of the mold cavity, flatness of the parting surface, and positional accuracy of the positioning hole.
The measuring points should cover the functional surface
The wheel rim curve, spoke surface, and sprue area of the cavity are functional surfaces that must be dotted.
The flatness of the parting surface directly affects the joint, and the measuring points should be evenly distributed along the parting surface with a spacing of no more than 100mm.
The positional accuracy of the positioning hole and the guide column hole determines the precision of mold clamping and is a necessary measurement item.
Establishment of benchmarks
The benchmark should be consistent with the drawing annotations. The benchmark is wrong, all data is meaningless.
The benchmark of the mold is usually the bottom surface and two positioning holes. When establishing a benchmark, it is necessary to confirm the roundness of the hole, as roundness differences can affect the benchmark accuracy.
Xinfeng Mold will attach a three coordinate report when delivering the wheel hub mold, indicating the benchmark and measurement point numbers for customer review.
Matching accuracy with environment
The accuracy of the three coordinate system is often in the 0.005mm range, but the ambient temperature can affect the results. It is recommended to control the temperature in the measurement room at 20 ± 2 ℃.
The mold needs to be isothermal for at least 4 hours when moved from the workshop to the measurement room. Testing without isothermal conditions may result in a deviation of 0.01-0.03mm in the data.
The measurement range of large-sized molds should cover the entire cavity. When the itinerary is insufficient, it is necessary to measure in sections and then splice them together.
How to read the report
Look at the distribution of deviations, not just the maximum value. Deviation concentrated in a certain area indicates a systematic problem with processing or compensation.
See repeatability. Three measurements taken at the same location with a difference of more than 0.01mm indicate unstable measurement or clamping.
Watch the trend. The deviation along the wheel rim is periodic, which may be a problem with the machine tool's rotational accuracy.
Judgment of acceptance
The key dimensions are determined according to the tolerance on the drawing. The precision of mold manufacturing should be 2-3 levels higher than the requirements for castings.
The flatness of the parting surface is often required to be within 0.03mm. Exceeding the tolerance can lead to thickening of the seam.
The positional accuracy should be determined according to the maximum entity requirement, and compensation should be paid attention to.
Reuse of measurement programs
The same round of molds can reuse measurement programs to reduce programming time. The program should include benchmarks, measurement points, and evaluation methods.
Program versions need to be managed. If the program is not updated after the mold change, the measurement results will be distorted.
Data integration with suppliers
When customers and mold factories use different software, they need to unify the data format. The STEP format is commonly used to exchange 3D data.
Three coordinate measuring needles need to be regularly calibrated, and a needle tip wear of 0.01mm can cause significant measurement deviations.
The measurement report should be accompanied by a schematic diagram of the measurement points, only providing numbers, and the customer cannot determine where the measurement is.
Frequently Asked Questions
The first is to only test areas that are easy to measure. Difficult to measure surfaces are often the key.
The second is to use calipers instead of three coordinates. The accuracy and repeatability of the caliper are insufficient.
The third is not to record the measurement point number. The data cannot be reproduced, and there is a lack of basis for disputes.
Frequently Asked Questions
Q: What are the three coordinate measurements for?
Answer: Key dimensions of the mold cavity, flatness of the parting surface, and positional accuracy of the positioning hole.
Q: What are the temperature requirements for the measurement room?
Answer: It is recommended to keep the temperature at 20 ± 2 ℃ and keep the mold isothermal for 4 hours.
Question: What is the accuracy?
Answer: The equipment is often at the 0.005mm level and is actually affected by the environment.
Q: What do you think of the report?
Answer: When looking at the distribution and trend of deviations, it's not just about looking at the maximum value.
Question: What are the flatness requirements for the parting surface?
Answer: It is often required to be within 0.03mm.
Q: Can calipers be replaced?
Answer: No, the accuracy and repeatability are not enough.
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