Technical Guidelines for Precision Process and Quality of Mold Base Manufacturing

Mold base manufacturing, which is the foundation of successful injection molding, is a key process that goes beyond simple metal processing to determine the durability and precision of molds. The minute errors that occur when manufacturing the mold base are not only directly linked to the defects of the final injection product, but are also a major cause of shortening the life of the mold. Therefore, experienced engineers and purchasing decision makers must systematically understand the entire process from material selection to heat treatment and precision processing, and select the optimal production partner. This guide covers the technical elements and process-specific precautions that must be considered for the production of high-quality mold bases in depth.

1. Material Selection and Heat Treatment Characteristics for Mold Base Manufacturing

The first step in the mold base production is to select the steel that meets the mold's purpose and injection environment. Generally used S50C (Carbon Steel for Mechanical Structures) is highly processable and economical, but if mass production or high-pressure injection is required, Freeharden Steel P20 (718HH) or SKD61 (Comprehensive Alloy Tool Steel), a high-hardness steel material, should be considered. The choice of steel directly affects the cost of manufacturing the mold base, but long-term mold maintenance cost and production stability should be prioritized over initial cost reduction.

In particular, for large mold bases or precision injection bases, the management of residual stress generated after processing is essential. If the stress relief process is omitted after rough processing, the base may be deformed during subsequent precision processing steps or actual injection operation, which may lead to misalignment of the center. Professional manufacturers such as SGMOLD strictly manage the heat treatment conditions before and after processing in consideration of the physical properties of these materials and focus on ensuring the organizational stability inside the materials.

2. Key to precision processing: 6-sided polishing and tolerance management

The quality of the mold base fabrication process is determined by the parallelism and squareness of the base. The six-sided polishing process is to set the reference plane for all processing, and usually a precise tolerance within ±0.01mm should be maintained. If the reference plane is not accurate, accumulated errors will occur in the subsequent CNC milling, bore, and wire cutting processes, which cause a minute gap between the upper and lower plates when assembling the mold, causing a flash in the parting line.

In the MCT (Merning Center) machining stage, the placement of the coolant line and the processing of the guide pin bush hole are key. For the cooling circuit, deep hole drilling technology is required to prevent eccentricity during drilling, and the cooling efficiency should be maximized by minimizing horizontal and vertical errors. In addition, since the guide pin hole must ensure the perfect concentricity of the upper and lower plates, it is common to perform precision machining at ±0.005mm using a jig boring machine or high precision CNC equipment.

3. Design and fabrication considering thermal expansion and dimensional stability

During the injection molding process, the mold base is exposed to continuous thermal cycles. As the mold temperature rises, thermal expansion of the steel material occurs, which can lead to increased friction between guide parts or poor operation of the slide core. Therefore, when manufacturing the mold base, not only the dimensions at room temperature but also the clearance design considering the coefficient of thermal expansion at the operating temperature should be reflected.

Professional mold base manufacturers set processing tolerances by predicting the behavior of materials based on molding temperature. For example, for molds using high-temperature resins, the tolerance of the slide surface is set more freely than it is in the normal case, or a copper alloy bush with strong abrasion resistance is applied to prevent heat-induced seizure. These fine adjustments reduce trial and error that may occur during the initial operation of the mold and enable a quick transition to the mass production system.

4. Case Study: A Scenario for Resolving Flatness Unbalance in Large Mold Bases

One of the common problems in the manufacturing of large mold bases for automobile bumpers is the 'bending phenomenon' that occurs after processing. A domestic manufacturer found a flatness defect in which the center of the top plate was lifted by 0.05 mm during the inspection stage after processing was completed. This was the result of the processing stress generated during the pocket processing process, which removes a large amount of material, combined with the internal residual stress.

To address this issue, SG MOLD's engineering team introduced the 'Vibration Stress Elimination (VSR) process to redistribute the stress of the material instead of the immediate calibration polishing and then re-performed the fine precision polishing. In addition, the stress concentration was distributed by changing the machining order from the outside to the symmetrical machining method instead of the inside. As a result, the final flatness was recovered to within 0.015mm, which is evaluated as an example of achieving extremely unusual precision despite being a large mold. The key indicator of the selection of mold base partners is whether or not to have a machining database that can cope with such sudden technical variables.

5. Frequently Asked Questions (FAQ)

Q1. What is the biggest factor in determining the cost of making a mold base?

A1. Material type (S50C vs. Freeharden Steel), base specification (size and thickness), and processing complexity. In particular, the cost varies greatly depending on the complexity of the cooling circuit, the presence or absence of precision boring, or the inclusion of special heat treatment.

Q2. How long does it usually take to produce?

A2. The type non-standard mold base can usually be manufactured within 5-7 days and can take 2-3 weeks or longer for custom manufacturing using special steel or involving complex 3D processing and heat treatment.

Q3. Is it possible to make a precision mold with S50C material?

A3. It is possible, however, because the S50C is less rigid, it is important to use high-hardness parts for key humidifiers such as guide pins and bushes and to ensure a reference plane through precise six-sided polishing.

Q4. What items should be included in the inspection report after mold base processing?

A4. Dimension accuracy of the main part, parallel and perpendicularity of each plate, position tolerance of the guide pinhole, and mill sheet and heat treatment hardness (HRC) measurements of the material used must be included.

6. Conclusion: Importance of a Trusted Moldbase Production Partner

The mold base is not just a mold frame for mold parts, it is a basic structure that can withstand injection pressure, dissipate heat, and support precise repetitive motion. If a manufacturer that lacks technical understanding only emphasizes low cost, it will eventually lead to higher costs due to frequent failures and poor quality at the injection site.

Based on decades of accumulated processing data and state-of-the-art facilities, SGMOLD provides an optimal mold base production solution by accurately grasping the customer's mold design intentions. A rigorous quality management system towards zero processing error will be a powerful asset to support your project's success.

If you need specific machining design review or technical advice on material selection for the ongoing project, please consult with SGMOLD's professional engineer group. I will suggest the most efficient and economical production plan through the review of the drawings.