I. Introduction

In numerous industries nowadays, portable handheld instruments play an indispensable role, and the injection molding of their housings is a crucial link. A high-quality injection molding process can ensure the precision, strength, and aesthetics of the housings, which directly affects the performance and user experience of the instruments. However, there are numerous difficulties in this process, and this article will conduct an in-depth analysis on them to explore effective solutions.

II. Difficulties and Solutions in Material Selection and Performance Balance

1. Difficulties

1.1 Material Adaptation Challenges 

Plastic materials are rich and diverse, each with unique physical and chemical properties such as strength, toughness, weather resistance, and transparency. When selecting materials for portable handheld instrument housings, it is necessary to meet the basic functions of protecting internal components and facilitating handheld operation while controlling costs. It is quite challenging to accurately select suitable materials.

1.2 Complex Performance Evaluation 

Accurately evaluating the performance of different materials under actual working conditions requires a large amount of test data and rich practical experience. It is also necessary to fully consider the compatibility between materials and internal instrument components to avoid component damage or performance degradation caused by chemical or physical reactions.

2. Solutions

2.1 In-depth Understanding of Material Properties

Analysis of Common Materials:

 ABS: It has good comprehensive physical properties, excellent strength and toughness, good processing performance, moderate requirements for temperature and pressure, relatively affordable cost, and can effectively protect components and is conducive to injection molding production.

PC: It has outstanding impact resistance and high transparency, but requires a high processing temperature and has a relatively high cost. When applying it, the performance and cost need to be weighed.

2.2 Selecting Materials by Comprehensively Considering Multiple Factors

Matching Performance Requirements: 

Analyze the usage scenarios of the instruments. For example, for outdoor monitoring, select materials with good weather resistance (such as modified PC); for those prone to collisions, select materials with good strength and toughness (such as ABS or modified materials). Consider special performance requirements. For components sensitive to static electricity, select anti-static materials (such as anti-static ABS or materials with added anti-static agents).

Weighing Cost Factors: 

Comprehensively evaluate the purchase price of materials, processing costs, scrap rates, material utilization rates, etc. Different materials have different processing requirements, which affect costs such as energy consumption; a high scrap rate will increase the unit cost; and the difficulty of recycling waste materials should be considered.

Ensuring Compatibility: 

Sort out and analyze the characteristics of internal instrument components, consult relevant materials or conduct tests to ensure that there are no chemical reactions or adverse physical interactions between the selected materials and the components, such as anti-corrosion and matching of thermal expansion coefficients.

III. Precision in Mold Design and Manufacturing

1. Difficulties

1.1 Design Adaptation Challenges 

The housings of portable handheld instruments have diverse shapes, and precise installation spaces need to be reserved for components such as batteries, circuit boards, and display screens inside. If the mold design is unreasonable, the injection-molded housings will not be well-matched with the internal components, resulting in problems such as difficult assembly, loose components, or even damage.

1.2 Manufacturing Precision Challenges 

During the mold manufacturing process, it is difficult to achieve high-precision dimension control. Even minor dimension deviations may affect the appearance quality of the housings, such as causing surface unevenness and excessive gaps, and also have an adverse impact on the functions of the housings, such as affecting the stability of component installation. Achieving high-precision manufacturing requires advanced equipment and exquisite techniques, which are often accompanied by high costs and technical thresholds.

1.3 Complexity of Demolding Design 

Designing a mold that can meet the requirements of the complex shape and internal structure of the housing and ensure efficient demolding is quite challenging. Different housing structures may require the use of special demolding mechanisms such as side ejection and inclined ejection. If the demolding method is not properly designed, the molded housing will be difficult to be smoothly ejected from the mold, which may lead to housing damage or low production efficiency.

2. Solutions

2.1 Following Mold Design Principles

Matching of Shape and Dimensions: 

The cavity shape of the mold must accurately correspond to the outer contour of the portable handheld instrument housing. Strictly control the dimension tolerance of the cavity to ensure the dimension accuracy of the housing so that it can be accurately assembled with the internal components. For example, for a specific handheld instrument housing, the key dimension tolerance of its mold cavity can be controlled within ±0.1 mm. Reserve sufficient and reasonable installation spaces for internal components and design structures such as card slots and positioning holes to facilitate the installation and fixation of components in the housing.

2.2 Adoping High-Precision Manufacturing Methods

Utilization of Advanced Equipment:

 Use CNC machining centers for rough and finish machining of molds. By precisely controlling the movement trajectory of cutting tools, high-precision dimension processing can be achieved. For complex mold structures, combine special machining methods such as electrical discharge machining to complete the parts that are difficult to achieve by conventional machining.

Quality Monitoring and Assurance: Regularly calibrate and maintain the processing equipment to ensure the stability of its processing accuracy. Use precision measuring equipment such as coordinate measuring machines to measure and feed back the key dimensions of the mold in real time to promptly detect and correct dimension deviations.

IV. Quality Control and Defect Prevention

1. Difficulties

1.1 Significant Impact of Common Defects 

Common quality defects in injection-molded products (such as bubbles, silver streaks, shrinkage, and flash) are prone to occur in the injection molding of portable handheld instrument housings. These defects not only affect the appearance quality of the housings but also reduce their mechanical properties and functional reliability, leading to unqualified products, increased scrap rates, and production costs.

1.2 Difficulty in Controlling Defect Causes 

It is quite difficult to accurately identify the causes of various quality defects and take effective preventive measures. Different defects are caused by multiple factors. A thorough understanding of each link of the injection molding process (such as raw material treatment, mold design, and injection molding operation) is required to prevent defects from the source.

2. Solutions

2.1 In-depth Analysis of Defect Causes and Preventive Measures

Bubbles:

 Causes: The raw material is not fully dried, and the water vaporizes during injection molding to form bubbles. The air cannot be discharged in time during the injection molding process and is wrapped by the plastic melt to form bubbles. The injection speed is too fast, and the melt generates turbulence in the cavity to entrain air to form bubbles.

Preventive Measures: Strengthen the drying treatment of raw materials to ensure that the water content is lower than the specified value. Set exhaust grooves on the mold. Reasonably adjust the injection speed.

Silver Streaks: 

Causes: The impurity content in the raw material is too high, and it is not evenly mixed with the plastic melt to produce silver streak phenomena. The temperature control is improper, such as the barrel temperature being too high or the mold temperature being too low, which causes the state of the plastic melt to change and produce silver streaks.

Preventive Measures: Strictly screen the raw materials to remove impurities. Precisely control the barrel temperature and mold temperature. Set appropriate temperature ranges according to different materials and mold structures.

Shrinkage: 

Causes: The holding pressure is insufficient or the holding time is too short, and the plastic cannot get enough compensation during the cooling and shrinking process, resulting in depressions on the surface of the housing.

Preventive Measures: According to the wall thickness of the housing and the shrinkage rate of the plastic raw material, reasonably set the holding pressure and holding time.

Flash: 

Causes: The clamping force of the mold is insufficient, and the plastic overflows from the mold cavity during the injection molding process to form excess plastic. The parting surface design of the mold is unreasonable, which makes the plastic easy to accumulate on the parting surface to form excess plastic.

Preventive Measures: Ensure that the clamping force of the mold is sufficient. Calculate the appropriate clamping force according to the size of the mold and the injection pressure and regularly check it. Optimize the parting surface design of the mold and adopt appropriate sealing measures to prevent the accumulation of plastic.

V. Conclusion

In conclusion, although the injection molding of portable handheld instrument housings is of great importance in various industries, it faces difficulties such as material selection, mold precision, process parameter optimization, quality control, and cost control. Through in-depth analysis of each problem and corresponding solutions, it is hoped that practitioners can effectively address these issues, improve product quality and market competitiveness, and promote the continuous development of the industry.