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Speaker component manufacturing requires high-precision assembly to prevent defects. Also, there is a need to balance between rigid materials that support sound quality and manufacturing complexities. The client walked into First Mold’s facility hoping to strike a lasting relationship with a company that could help them overcome these challenges.

Sink marks, weld lines, and warping are some of the unresolvable challenges the client had with their former supplier, which necessitated the search for a new partner. For the client, the right speaker injection molding solution should not be just about flipping materials. They wanted a manufacturer that understood design for manufacturability as a key component of cutting costs for long-term product sustainability in a competitive market.

Challenges

The first challenge with audio parts manufacturing is the high tolerance (0.05 mm to 0.025 mm) requirement for high-precision parts. This is particularly true for critical acoustic and assembly components to avoid sound leaking, which will affect the sound quality. The tolerance for non-critical parts like the reflex ports and internal chambers can be relaxed to 0.1 mm. Understanding the tolerance requirements of the different parts is critical in speaker mold manufacturing.

As little as a 0.1 mm deviation in speaker injection mold accuracy can lead to poor sound performance. Some of the common faults that can result from inaccurate mold tolerance, especially in smaller speakers, include air leaks, unwanted vibrations, and distortion. Other critical considerations that First Mold engineers had to factor into the planning phase of the client’s loudspeaker parts manufacturing include:

• Shrinkage control: Crystalline materials like polypropylene (PP) can shrink as much as 1.8%. On the other hand, amorphous materials like polycarbonates (PC) and acrylonitrile butadiene styrene (ABS) shrink less, usually 0.3-0.7%.
• Wall thickness: The wall thickness is a crucial consideration in speaker production. A 0.1 mm deviation in wall thickness can lead to significant sound distortion.

After several meetings with the client and extensively analyzing the product blueprint and how speaker is made, First Mold engineers identified five high-level challenges that needed to be addressed.

1. Structural and Acoustic Performance

The speaker enclosure manufacturing must be done with materials that would be rigid enough to prevent flex, but dampened enough to avoid audible vibrations that distort sound. Flaws in enclosure design can create situations where vibrations from the speaker travel through the material, creating acoustic feedback. This lowers the efficacy of active noise cancellation.

2. Material Selection and Limitation

First Mold engineers had to consider the peculiar challenges associated with different materials and factor them into the speaker mold design. For example, some PP materials are difficult to paint, while others are more difficult to mold into complex shapes. Resins like polyetherimide with superior acoustic properties require an expensive tooling process and very high temperatures to mold.

3. Injection Molding Defects

Manufacturing of speaker enclosures often features ribs and bosses for mounting speakers. The thick sections around ribs can develop sink marks if the molding process is not properly controlled. Also, inconsistent shrinkage during cooling can lead to enclosure warping. The outcome is improper sealing, which will ruin the bass performance. Preventing weld lines in speakers is crucial because they create weak points that vibrate or break under high-volume pressure.

4. Assembly Challenges

After manufacturing speaker components, the parts are assembled. The client specifically wanted their product to meet IPX7 standards. This required perfect airtight seals. First Mold engineers determined that the first step to achieving airtight seals is through extremely tight tolerances during molding. Some metal voice coil components need to be inserted into the mold and overmolded. Catastrophic component failure can result from insert misalignment.

5. Ensuring Production Efficiency

Speaker mold manufacturing with high precision is expensive and time-consuming. Adapting rapid design changes is difficult. Also, it was necessary to optimize cycle time to cut production costs in the long term. One of the ways to reduce costs is through faster injection speeds. However, it can cause material degradation, air traps, or burn marks. Therefore, it was necessary to derive new ways to optimize the client’s speaker component manufacturing to prevent these issues.

Solution

Working closely with the client, First Mold engineers designed a suite of comprehensive solutions to resolve all the identified loudspeaker parts manufacturing challenges. The speaker component production was carried out with full consideration of the IEC 60268 standards. The entire production process was also done in compliance with the ISO 13485 quality management system to ensure the highest product quality and user safety.

Tooling

The client’s blueprint identified PP as the primary material that will be used for speaker enclosure manufacturing. Therefore, the speaker mold production was optimized with this material in mind. Some of the key considerations First Mold engineers made include:

• Wall thickness: First Mold maintained a uniform wall thickness of 2 mm. This was necessary to prevent uneven cooling that leads to sink marks and warpage. Ribs were added to thick sections to maintain nominal thickness.
• Draft angles: A 1^o draft angle was added on all vertical walls to ensure smooth ejection. This was also necessary to protect the surface from drag marks.
• Gate design and positioning: First Mold incorporated larger gates in the speaker mold manufacturing. Larger gates compensated for PP’s flow characteristics and led to a reduction in internal stress. Also, the gates were strategically located in thicker areas to ensure proper packing and reduce the risk of sink marks.
• Venting: First Mold engineers added improved air vents at the end of the flow path. The improved venting system was more efficient at allowing trapped gas to escape, thus preventing incomplete filling (short shots) and burn marks.
• Shrinkage allowance: To ensure dimensional accuracy, the design was done to accommodate the high shrinkage potential of PP.
• Cooling system Optimization: First Mold engineers reimagined the cooling system through the creation of efficient cooling channels. This was crucial in ensuring uniform cooling. Uneven cooling leads to thermal distortion and high shrinkage in semi-crystalline materials.
• Surface treatment: The speaker injection molding was expected to have a gloss finish. Since PP accurately replicates mold surfaces, the mold core was polished to achieve a gloss finish.

First Mold’s efficient mold design eliminated the formation of defects. Also, the tight tolerances achieved with the mold design made it easier to achieve a tight seal to meet the IPX7 waterproofing standards.

Advanced Mold Testing

After building the speaker mold, it was put through a series of tests for validation, starting with pre-trial inspection. The dimensions and specifications were tested to ensure the mold cavity and core aligned with the blueprint, using coordinate measuring machines (CMM).

This was followed by the verification of the hardness of the steel components, including sliders, cavity, and core, to ensure their durability. The cooling water channels were pressure-tested to ensure there are no leaks in the circulation. The sliders, lifters, and ejector pins were properly lubricated and manually checked to ensure smooth movement.

Initial Mold Trial

The test speaker injection molding, or T0, was conducted with a focus on basic functionality. The follow-up T1 trial focused on quality. Functional tests inspected the efficacy of the ejection system and the motion of the moving parts under normal operating pressure. Other tests conducted included the filling test, venting inspection, and parting line inspection.

A detailed measurement of the produced part was conducted to ensure it met all critical dimensions, tolerances, and design specifications. First Mold quality assurance team also conducted weight verification to check for consistency, which indicates proper material density and packing pressure.

Speaker Injection Molding Process Optimization

First Mold’s rigorous testing ended with the documentation of the ideal settings, including temperature, pressure, speed, and cooling, for consistent production. The goal was to get the mold ready for high-volume production and avoid costly downtime.

What The Client Gained By Working With First Mold

The client received optimized molds in a timely manner, which allowed them to create custom parts, including speaker dust cap manufacturing. The mold was carefully designed to address all the challenges facing the unique design of the client’s speaker. During the mold delivery, the client received detailed documentation that will help them to optimize production and extend the lifespan of the mold.

Another benefit the client received from working with First Mold was after-sales support, including ordering replacement parts. This case marked the start of a long-lasting relationship. First Mold has since created over 150 sets of molds for the client, spanning over 30 different audio product models.

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