上个月，一个做协作机器人关节模组的客户，寄来一只外壳的样件。
黑色的，巴掌大，是关节模组的外罩。他说打出来表面发白发毛，喷漆挂不住，客户那边拒收。他在微信里发了句原话："你这玻纤加多了吧，换个低玻纤的料。"
我让他把模温表拍过来。他发来一张截图：80℃。
这壳子不是玻纤加多了，是模温太低，把玻纤冻在了表面上。
关节模组外壳这件改性尼龙，最容易背的锅就是"玻纤多"。其实很多时候，锅在工艺上。
一、外壳这件"皮"，比你想的难做
先把关节壳在模组里的位置说清。
关节模组是电机 + 减速器 + 编码器的集合体，外壳就是包住它们的那层"皮"。它不传力，但要把电机的热、编码器的精度、走线的空间，全都安顿好。
这个角色带来一个后果：壳子的失效，绝大多数不是"破了"，是"变形、缩水、表面丑"。
具体是三件麻烦事：
尺寸。 壳子要和内部件严丝合缝，孔位、止口差 0.1 mm 就装不上。
翘曲。 大平板、薄壁壳注塑出来会扭，装配时靠螺钉硬拉，拉出内应力。
表面。 浮纤、缩痕、熔接线，在外观件上全是拒收理由。
所以问"关节壳用什么料"，问法偏了。 该问的是：这件壳子的壁厚、孔位和表面，哪一条先爆。
二、外壳的六类约束
壳子看着简单，工况其实被六条线拽着。
温度。 电机贴在壳子里壁，局部温度能到 80–100℃，连续运行更高。壳子要扛得住长期热，还不能把热闷死。
载荷。 壳子本身不受大载，但螺钉紧固、跌落冲击、搬运磕碰都要算。
电磁。 编码器和电机对干扰敏感，部分壳子要加导电填料做屏蔽，或者留金属嵌件。
介质。 车间油污、手部油脂、清洁剂，都对表面有要求。
寿命。 启停以百万次计，判据是"到寿命时尺寸和外观还行不行"。
外观。 协作机器人露在外面的壳，浮纤、色差、缩痕都要控。这一条比内部支撑件较真得多。
六类里，温度和尺寸是硬门槛，电磁和外观决定方案能不能收口。
三、壳体材料的几条路线
从金属换塑料，壳子的逻辑和臂杆不同——它不太要刚性，要的是尺寸稳、好成型、表面能看。
| 路线 | 组成 | 给什么 | 代价 |
|---|
| 增韧 PA6 | 弹性体增韧 | 抗冲击、好喷涂、低气味 | 刚性低、耐温一般 |
| PA66-GF30 | 中玻纤 + 稳定 | 尺寸稳、耐温好、刚性够 | 表面浮纤、要控模温 |
| PA/ABS | 合金 | 外观好、易着色 | 耐温偏低、改性复杂 |
三条没有"谁更好"，只有"这个壳子要不要刚性"。
增韧 PA6 这一行，是外观壳的主力。抗冲击、表面好处理、气味低，做协作机器人露脸的件比 PA66 好看。代价是刚性和耐温一般，内部支撑件要用得谨慎。
PA66-GF30 这一行，尺寸稳定性和耐温更好，适合既要包住电机又要一定刚性的壳。代价是表面浮纤，模温和工艺要管住。
PA/ABS 这一行，外观和着色最顺，但耐温偏低，靠近电机的壳要避开。
壳子的壁厚不是单独定的，它和玻纤含量互相牵。
薄壁壳要流动好，玻纤含量就得往下降，刚性跟着让一点。
厚一点的壳可以吃高玻纤，尺寸更稳，但冷却慢、缩痕风险上来。
这两件事要摆在工艺窗口里一起排，不能先定料再定壁厚。
换料的时候，这个顺序尤其容易被跳过。
客户拿着旧壳子来问"能不能换成你们的料"，很少先量壁厚。
壁厚量完，能选的玻纤档位其实已经定了一半。
先量件，再选料，省下的是后面两轮试模。
一句话：壳子选料，先问"贴不贴电机、露不露脸"，再问牌号。贴电机看耐温，露脸看表面。
四、外壳选材判据表
把上面的约束落成可核对的指标。下表门限是方向性建议，不是验收标准——实际数值由具体项目、工况和实测定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 成型收缩率 | 按壁厚定，通常 0.4–0.8% | ISO 294 | 孔位偏、装不上 | 玻纤 + 低收缩体系 | 偶联剂（降取向差） |
| 平面度 / 翘曲 | 按件精度定，0.3 mm 量级起 | 三坐标实测 | 装配应力、异音 | 调浇口 + 提模温 | 偶联剂（界面） |
| 长期热变形 | 100℃×1000h 后尺寸稳 | ISO 75 | 软化、止口松 | 热稳定体系 | 抗氧剂（长期热氧） |
| 表面浮纤 | 目视 / 粗糙度达标 | 客户外观标准 | 喷漆挂不住、拒收 | 提模温 + 多级射胶 | 润滑剂（改善包覆） |
| 冲击强度 | 落锤按工况定 | ISO 179 | 跌落开裂 | 弹性体增韧 | 增韧剂（界面相容） |
| 壁厚均匀性 | 同一截面厚薄比 ≤1.5 | 剖切 / 超声测厚 | 缩痕、变形 | 筋位与壁厚过渡设计 | 助剂不担此责 |
| 流动性（薄壁） | 按壁厚与流程定 | 螺旋流动长度 | 短射、浮纤 | 降玻纤 / 提料温 | 润滑剂（内外润滑） |
| 电磁屏蔽（如需） | 按干扰等级定 | 阻抗测试 | 编码器误码 | 导电填料或嵌件 | 助剂不担此责 |
怎么用这张表：别逐行打分，先看第一行和第三行。尺寸和耐温过不去，表面再好看也没用。
浮纤的真凶：客户说"玻纤加多了"，我们常先查模温。高玻纤料熔体在模腔里是喷泉式流动，玻纤被推到前沿，一碰低温模壁就被冻住，树脂来不及包回去。把模温从 80℃ 提到 115℃，同一批料、同一个模具，浮纤基本消失。玻璃纤维被你加进去，又被你冻在了表面上。
五、外壳常见的五处翻车
翻车一：孔位偏，装不上。
根因常是收缩率没补偿。玻纤件各向异性，流动方向和垂直方向收缩不同，壳子上的孔位会整体飘。先按件做收缩补偿，不套手册通用值。
翻车二：翘曲，螺钉硬拉出应力。
根因是浇口位置和模温。大平板壳翘曲最敏感，翘的方向和流动方向一致 → 先查浇口，不查配方。
翻车三：表面发白喷不上漆。
根因多半是模温低冻住玻纤（见第四节）。不是换低玻纤料，是提模温、改多级射胶。
翻车四：同一批件色差。
不是"料不稳定"，是色母或抗氧剂分散不均。先查混料与母粒化，别急着换料。
翻车五：装完有异响，拆开看是内应力。
根因常是翘曲件被螺钉硬拉到位，装配应力存进了件里。
跑起来温度一变，应力释放，件变形蹭到旁边的件。
这种问题不在料上，在平面度和装配方式上。
这里要直说：壳子件的失效排查，先怀疑工艺与后处理，最后才怀疑材料。 把浮纤说成"玻纤多"去换料，往往是用错的解法。
六、壁厚、一体成型与后处理
壁厚。 壳子壁厚定均匀，骤厚骤薄会缩痕和翘曲。薄壁壳（1.5–2.5 mm）要料流动性好，模温足。
一体成型。 把支架、卡扣、走线槽做进壳子，能省装配，但模具复杂、排气要足。一体成型的壳，浇口和排气设计比材料更关键。
嵌件。 金属嵌件（轴承室、螺钉柱）和塑料收缩不同，冷缩会裂。嵌件预热、留收缩间隙，是老经验。
排气。 一体成型和深蚀纹的壳最容易困气，困气处发白、烧焦。
排气槽要开到料流末端，模温高的位置更要留足。
排气不良的壳，表面处理再怎么调也救不回来。
调湿。 精密壳子要控状态。给客户的尺寸，应当是调湿之后测出来的那一组。
验证顺序。 建议这样排：
1. 尺寸与孔位（调湿后测，干态只作过程记录）
2. 平面度 / 翘曲（三坐标）
3. 表面（浮纤、缩痕、熔接线）
4. 装配（装内部件，测干涉）
5. 环境叠加（温湿循环 + 跌落）
顺序不能换。 前一项不通过就往下走，后面数据没有解释意义。
打样实录：有客户把壳子表面发白当成料的问题，要换低玻纤。我们把模温表一查——80℃。提到 115℃，同一批料、同一个模具，浮纤基本消失，喷漆一次过。后来我们把这件事写进打样确认单：先让客户把"模温多少"说清，再谈换料。
七、边界：哪些外壳还该用金属
这一段可能比前面六段更值钱。
以下四种情况，关节壳走尼龙这条路不建议推进：
其一，长期贴电机且内壁温度超过 130℃。 PA66 体系在这个区间长期保持数据支撑不足，要回到 PA6T / PA9T 或金属。
其二，要求气密或液密的结构壳。 塑料壳的焊接和密封比金属难，这类件要先验证密封工艺。
其三，高电磁屏蔽且不允许嵌件。 尼龙本身不导电，全靠导电填料或嵌件。不能嵌件又要强屏蔽，这条路难走。
其四，薄壁大平面且高精度孔位。 注塑薄壁大平面的尺寸和翘曲极难控，这类件要先做工艺可行性。
把这四条写在前头，不是劝退，是省时间。 样品阶段一路顺、最后卡在密封或尺寸上、整个方案回退的项目，我见过不止一个。
换料风险清单（从金属换到尼龙壳体，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 孔位按件做收缩补偿，排气重做 | 薄壁大平面排气不足 |
| 干燥 | 按实测含水率定窗口 | 回用料掺入带入水分 |
| 料温 / 模温 | 按表面质量定模温（常 110℃+） | 只按牌号推荐值给 |
| 保压 / 脱模 | 薄壁壳保压曲线重定 | 缩痕、变形 |
| 调湿 | 强制调湿 + 称重 + 复测 | 按平均壁厚估时间 |
| 色差 | 外观件色板提前确认 | 高玻纤件本身发暗 |
| 验证顺序 | 尺寸 → 翘曲 → 表面 → 装配 → 环境 | 前一项未过就往下走 |
打样试模排程
| 轮次 | 上机内容 | 每轮验什么 | 留样 |
|---|
| 第一轮 | 螺杆试小样，短射看填充 | 薄壁是否打满、浮纤 | 留 3 件，3 个月 |
| 第二轮 | 正式试模，调模温保压 | 孔位、平面度（干态） | 留 5 件，6 个月 |
| 第三轮 | 调湿后复测 + 装配验证 | 孔位（湿态）、干涉 | 留 8 件，12 个月 |
一页纸汇报表（给要向上汇报的人）
`
项目：关节模组外壳 · 尼龙壳体路线评估
结论方向：可作为候选路线，能否落地取决于三项前置条件
一、必须守住的三条
1. 孔位按件做收缩补偿，不套通用值
2. 模温按表面质量定（常 110℃ 以上）
3. 尺寸报告按调湿态出，干态只作过程记录
二、前置条件（任一不满足则建议暂缓）
· 内壁长期温度 ≤ 130℃ 量级
· 不要求气密 / 液密结构
· 屏蔽要求可用嵌件或填料满足
· 壁厚与孔位工艺可行
三、下一步动作
1. 取金属壳，测孔位与止口
2. 定壁厚与浇口方案
3. 调湿前后三坐标复测
风险提示：本路线主要不确定性在表面质量与翘曲，不在初始强度。
`
读者常问的三句
问：和进口料差在哪？
只讲两件能对照的事：同一指标，看它标没标测试条件；同一件上，看它给没给长期数据。壳体类指标对模温和状态敏感，条件不明的数字不宜直接比。有些件上走国产路线已经比较成熟，有些件目前仍不建议替——具体到你的壳，要看贴不贴电机、露不露脸两样。
问：能不能一体成型省装配？
能，但要先付模具和工艺的代价。一体成型的壳，浇口、排气、镶件都比分件难，验证要重做。先算装配省下的钱够不够覆盖模具增量，再决定。
问：壳子的色差能控到什么程度？
色差要分两件事看：料本身的批次差，和工艺造成的深浅差。
料端靠色母与混料稳定，工艺端靠模温与保压一致。
外观壳要提前做色板确认，把标准和判级方法写进技术协议。
没有色板的壳，批量一定吵。
结语
关节模组外壳的塑化，说到底是一道尺寸与表面的题，不是强度题。
判断链只有三条：
温度定基材 → 壁厚定工艺 → 模温定表面。
三条都定完，"能不能用塑料"这个问题自然就有答案了。
如果你手上正有一个关节壳或模组外壳要定料，把三样东西发过来就能给方向：内壁温度、壁厚与孔位、是否露脸。
还有一句要补上：壳子这件"皮"，最贵的一次往往不是料钱，是量产之后才发现表面过不了。
前期多花两周做模温和排气，比后期返工便宜得多。
料是同一个料，工艺是两套工艺。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 和尼龙合金这些树脂，改成某个件真正能用的样子；顺带做改性 PPO、PPS 和热塑性弹性体；也经营各大化工巨头的尼龙树脂、副牌料和大包料，另长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
配方里的助剂体系按件的工况配——常规助剂常备现货，特殊型号按需配套；你报工况和牌号，料和助剂一次配齐。
Last month, a customer who makes collaborative robot joint modules sent a sample of a casing.
It's black, palm-sized, and is the outer cover of a joint module. He said that when it was molded, the surface turned white and fuzzy, paint wouldn't stick, and the client refused to accept it. He sent a message on WeChat with the original words: 'You've added too much fiberglass here, switch to a material with less fiberglass.'
I asked him to send over the mold temperature gauge. He sent a screenshot: 80℃.
The shell isn’t made with extra fiberglass; the mold temperature is too low, which caused the fiberglass to freeze on the surface.
This modified nylon for joint module housings is most easily blamed for having 'too much glass fiber.' In fact, many times, the blame lies in the process.
1. The 'skin' of the shell is harder to make than you think
First clarify the position of the joint shell in the module.
The joint module is a combination of a motor, a reducer, and an encoder, and the casing is the 'skin' that wraps around them. It does not transmit force, but it needs to accommodate the motor's heat, the encoder's precision, and the space for wiring.
This character brings a consequence: shell failure, which in the vast majority of cases is not 'broken,' but 'deformed, shrunken, or with an ugly surface.'
Specifically, there are three troublesome matters:
Size. The casing must fit the internal parts perfectly; if the hole positions or stops are off by 0.1 mm, it won't fit.
Warping. Large flat plates and thin-walled shells will twist when injection molded, and during assembly, screws are used to forcibly pull them, creating internal stress.
Surface. Floating fibers, shrink marks, and weld lines are all reasons for rejection on exterior parts.
So asking 'what material is used for the joint shell' is the wrong way to ask. The question should be: for this shell, which aspect—wall thickness, hole positions, or surface—will fail first?
2. Six Types of Constraints on the Shell
The shell looks simple, but the working conditions are actually controlled by six lines.
Temperature. The motor is attached to the inner wall of the casing, and the local temperature can reach 80–100°C, even higher during continuous operation. The casing must withstand long-term heat and still not trap the heat completely.
Load. The shell itself does not bear a large load, but screw fastening, drop impact, and handling bumps all need to be considered.
Electromagnetic. Encoders and motors are sensitive to interference; some housings need to add conductive filler for shielding, or leave metal inserts.
Medium. Workshop oil, hand grease, and cleaning agents all have requirements for the surface.
Lifespan. The start-stop is measured in millions of times, and the criterion is 'whether the dimensions and appearance are still acceptable at the end of the lifespan'.
Appearance. The exposed shell of the collaborative robot must control floating fibers, color differences, and shrinkage marks. This is taken more seriously than the internal support components.
Among the six categories, temperature and size are hard thresholds, while electromagnetics and appearance determine whether the solution can be finalized.
3. Several approaches to shell materials
Switching from metal to plastic, the logic for the casing is different from the arm—it doesn't require much rigidity, but needs dimensional stability, ease of molding, and a surface that looks good.
| Route | compose; consist of | Give what | Cost |
|---|
| Toughened PA6 | Elastomer toughening | Impact-resistant, easy to spray, low odor | Low rigidity, average temperature resistance |
| PA66-GF30 | Medium Glass Fiber Stable | Stable dimensions, good temperature resistance, sufficient rigidity | Surface floating fibers, need to control mold temperature |
| PA/ABS | Alloy | Good appearance, easy to color | Low temperature resistance, complex modification |
The three don't have 'which is better,' only 'should this casing be rigid or not.'
The toughened PA6 line is the main material for outer shells. It has impact resistance, is easy to finish on the surface, and has low odor, making parts for collaborative robots look better than PA66. The trade-off is that its rigidity and heat resistance are average, so internal support parts need to be used cautiously.
For PA66-GF30, this type has better dimensional stability and heat resistance, suitable for enclosures that need to cover the motor while maintaining a certain rigidity. The downside is surface fiber bloom, so the mold temperature and process need to be controlled.
In the PA/ABS series, the appearance and coloring are the smoothest, but the temperature resistance is relatively low, so the housings near the motor should be avoided.
The thickness of the shell is not determined independently; it is interrelated with the glass fiber content.
For thin-walled shells to flow well, the glass fiber content has to be reduced, which in turn slightly lowers the rigidity.
A thicker shell can handle higher glass fiber content, making the dimensions more stable, but cooling is slower and the risk of sink marks increases.
These two matters should be arranged together at the process window; you cannot determine the material first and then the wall thickness.
During material changes, this step is particularly easy to be skipped.
Customers come with old shells asking 'Can this be replaced with your material?' and seldom measure the wall thickness first.
Once the wall thickness is measured, the selectable fiberglass grade is actually already half determined.
First measure the parts, then select the materials; what you save is the next two rounds of mold trials.
In one sentence: When selecting the shell material, first ask 'Will it be attached to the motor, or will it be exposed?', then ask about the grade. If attached to the motor, consider temperature resistance; if exposed, consider the surface.
4. Criteria Table for Shell Material Selection
Turn the above constraints into verifiable indicators. The thresholds in the table are directional suggestions, not acceptance standards — actual values are determined by specific projects, operating conditions, and measured data.
| Indicator | Directional Threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| Molding shrinkage | Based on wall thickness, usually 0.4–0.8% | ISO 294 | The hole position is off, cannot be installed | Fiberglass low-shrinkage system | Coupling agent (reduces orientation difference) |
| Flatness / Warping | Determined by part precision, starting from the 0.3 mm level | CMM measurement | Assembly stress, abnormal noise | Gate Adjustment Mold Release Temperature | Coupling agent (interface) |
| Long-term thermal deformation | Dimensions stable after 100℃ × 1000h | ISO 75 | Softening, stopping the mouth from loosening | Thermally stable system | Antioxidant (long-term thermo-oxidative) |
| Surface floating fibers | Visual / Roughness Standard Met | Customer appearance standards | Spray paint won't stick, refused | Mold removal temperature Multi-stage injection | Lubricant (improves coating) |
| Impact strength | Hammer drop is determined according to operating conditions | ISO 179 | Drop and crack | Elastomer toughening | Toughening agent (interface compatibility) |
| Wall thickness uniformity | Thickness ratio of the same cross-section ≤ 1.5 | Sectioning / Ultrasonic thickness measurement | Shrinkage and deformation | Rib position and wall thickness transition design | Additives not responsible |
| Flow (thin-walled) | Defined by wall thickness and process | Helical flow length | Short shot, floating fiber | Reduce glass fiber / lifting temperature | Lubricant (internal and external lubrication) |
| Electromagnetic shielding (if needed) | Set by interference level | Impedance testing | Encoder error code | Conductive packing or insert | Auxiliary not responsible |
How to use this table: Don't score line by line, first look at the first and third rows. If the size and temperature resistance don't pass, no matter how attractive the surface is, it won't help.
The real culprit of floating fiber: When customers say 'too much fiberglass,' we often check mold temperature first. High-grade glass fiber melt flows like a fountain inside the mold cavity, pushing the glass fiber to the front, and when it touches the low-temperature mold wall, it freezes, leaving the resin unable to wrap back in time. Raising the mold temperature from 80°C to 115°C, with the same batch of material and mold, the floating fibers basically disappear. You add glass fiber, but you freeze it on the surface again.
Five, Five Common Shell Failures
Misplacement One: Hole position is off, can't be installed.
The root cause is often lack of compensation for shrinkage. Fiberglass parts are anisotropy, and the flow direction and vertical contraction differ, causing the holes on the shell to float overall. First, compensate for shrinkage by piece, without applying the manual's general values.
Failure 2: Warping, screw forced pulling to release stress.
Root cause is gate position and mold temperature. Large flat shell warping is the most sensitive; warping direction and flow direction are consistent → Check gate first, not formula.
Failure 3: Surface whitening and no coating.
Root cause mostly is low mold temperature freezing glass fiber (see Section 4). Not replacing low fiberglass material, but raising mold temperature and changing to multi-stage injection adhesive.
Failure 4: Color difference in the same batch.
It's not 'unstable material', but uneven dispersion of masterbatch or antioxidant. First, check the mixing and masterbatch formation; don't rush to replace the material.
Failure 5: Abnormal noise after assembly; disassemble and find internal stress.
The root cause is often warped parts being forcibly pulled into place by screws, causing assembly stress to accumulate inside the part.
When running, the temperature changes, stress releases, and the part deforms and rubs against the adjacent part.
This problem isn't with the material, but with flatness and assembly method.
Here's a straightforward point: when checking failure of shell parts, first consider the process and post-processing, then the material. Calling floating fibers "too much fiberglass" for material exchange is often the wrong approach.
6. Wall thickness, integrated molding, and post-processing
Wall thickness. The shell wall thickness is uniform; sudden thickening and thinning can cause shrinkage marks and warping. Thin-walled shells (1.5–2.5 mm) require good material flow and sufficient mold temperature.
Integrated molding. Inserting brackets, clips, and cable trays into the shell saves assembly but requires complex molds and sufficient venting. For integrated shells, gate and vent design are more critical than materials.
Inserts. Metal inserts (bearing housing, screw posts) shrink differently from plastic and can crack when cold. Preheating inserts and leaving shrinkage gaps is an old practice.
Vent. Shells with one-piece molding and deep etching are most prone to air trapping; the trapped areas turn white and burn.
The vent groove should be opened to the end of the material flow, and the area with higher mold temperature must be left sufficiently.
Poorly vented shells cannot be saved no matter how much the surface treatment is adjusted.
Humidity control. Precision shells must be controlled in condition. The size given to customers should be the group measured after humidity adjustment.
Verification sequence. Suggested arrangement:
1. Dimensions and hole positions (measured after humidity adjustment, only recorded in dry state)
2. Flatness / warpage (coordinate measuring machines)
3. Surface (floating fibers, shrinkage marks, welding wires)
4. Assembly (internal components, interference testing)
5. Environmental overlay (temperature and humidity cycling + drop)
Sequence cannot be changed. If the first item fails, proceed downward; the later data is meaningless.
Prototyping record: Some customers mistakenly think the shell surface is white, and need to switch to low-grade fiberglass. We checked the mold temperature gauge—80°C. When it comes to 115°C, for the same batch of material and the same mold, the floating fibers basically disappear, and the painting is done in one go. Later, we wrote this into the sample confirmation form: first have the customer clearly state the "mold temperature," then discuss material replacement.
7. Boundaries: Which casings should still be made of metal ?
This section may be more valuable than the previous six segments.
In the following four situations, it is not recommended to go with nylon for joint shells:
First, long-term attachment to the motor and inner wall temperature exceeding 130°C. PA66 systems maintain insufficient data support in this range for a long time, so we need to return to PA6T / PA9T or metal.
Second, require airtight or liquid-tight structural shells. Welding and sealing plastic shells is more difficult than metal ones; for these parts, the sealing process must be verified first.
Third, high electromagnetic shielding and no inserts allowed. Nylon itself is non-conductive and relies entirely on conductive fillers or inserts. If inserts cannot be inserted but strong shielding is required, this path is difficult.
Fourth, thin-walled large flat surfaces with high-precision hole positioning. The size and warpage of injection-molded thin-walled large surfaces are extremely difficult to control, so these parts must first be made for process feasibility.
Writing these four points at the beginning is not to discourage them, but to save time. I have seen more than one project where the sample stage proceeds smoothly but ultimately gets stuck on sealing or dimensioning, causing the entire plan to regress.
Material replacement risk list (from metal to nylon housing, items to be moved)
| Steps | What to move | Points prone to leakage |
|---|
| Molds | Hole shrinkage compensation by piece, exhaust rework | Thin-walled large flat insufficient exhaust |
| Drying | Window set based on measured moisture content | Recycled material mixed in with moisture |
| Material temperature / mold temperature | Set mold temperature based on surface quality (constant 110°C+) | Only reset the pressure holding curve for |
| holding pressure / demolding | thin-walled shell based on recommended grade values | Shrinkage, deformation |
| Humidity adjustment | Forced humidity adjustment + weighing + retesting | Estimation time based on average wall thickness |
| Color difference | Appearance component color chart advance confirmation | High fiberglass parts themselves darkened |
| Verification sequence | Dimensions → Warpage → Surface → Assembly → Environment | If the previous item is not passed, proceed |
Prototyping and mold trial scheduling
| Rounds | Machine content | What to test each round | Sample retention |
|---|
| First round | Screw sample testing, short shot check filling | Is the thin wall fully sealed and the fibers floating ? | keep 3 pieces, 3 months |
| second round | formal trial mold, mold temperature and pressure adjustment | hole position, flatness (dry state) | keep 5 pieces, 6 months |
| third round | post-humidity retest + assembly verification | hole position (wet state), interference | Keep 8 items, 12 months |
One-page report form (for those reporting upward)
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Project: Joint module shell · Nylon housing route evaluation
Conclusion: Can be used as a candidate route; whether it can be implemented depends on three prerequisites
1 . Three essential points to be held
1. Hole positions compensate for shrinkage by piece, do not apply general values
2. Mold temperature is determined by surface quality (above constant 110°C)
3. Dimensional reports are issued according to humidity condition; dry state only records the process
2. Prerequisites (if any one is not met, postponement is recommended)
· Long-term inner wall temperature ≤ 130°C order
· No airtight / liquid-tight structure required
· Shielding requirements can be met by inserts or fillers
· Wall thickness and hole position process feasible
III. Next steps
1. Take a metal shell, measure hole position and stop hole
2. Set wall thickness and gate solution
3. Re-measure coordinate measuring before and after humidity adjustment
Risk warning: The main uncertainty of this route lies in surface quality and warpage, not in initial strength.
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Three Questions Readers Often Ask
Question: What's the difference from imported materials?
Let's just talk about two things you can compare: for the same indicator, check if it shows test conditions; For the same item, check if it provides long-term data. Shell indicators are sensitive to mold temperature and condition; numbers with unclear conditions shouldn't be compared directly. Some parts have already matured toward domestic production, while others are still not recommended for replacement—specifically, it depends on whether you stick the motor and show your face.
Question: Can it be molded in one piece to save assembly?
Yes, but you have to pay for molds and craftsmanship first. For one-piece shells, gates, vents, and inserts are all harder than splitting parts, so verification requires rework. First, calculate whether the cost saved from assembly is enough to cover the mold increment, then decide.
Question: How much color difference can be controlled for the shell?
Color difference needs to be checked in two ways: batch differences in the material itself and the depth differences caused by the process.
The material side relies on masterbatch and mixing stability on the material end, while the process side relies on mold temperature and holding pressure consistency.
For the appearance of the shell, make a color swatch in advance and include the standards and grading methods in the technical protocol.
Shells without color swatches will definitely cause disputes in batches.
Conclusion
Ultimately, the plasticization of joint module shells is a problem of size and surface, not strength.
There are only three judgment chains:
Temperature determines substrate → wall thickness determines process→ mold temperature determines surface.
Once all three are set, the question of "can plastic be used?" naturally has an answer.
If you have a joint shell or module shell to prescribe, send over three things and you can give directions: inner wall temperature, wall thickness and hole position, and whether the face is visible.
One more thing to add: the most expensive part of the shell's "skin" is often not the material cost, but the surface can't be passed after mass production.
Spend two extra weeks in the early stages working on mold temperature and venting, which is much cheaper than redoing later.
The material is the same material, but the process is two sets.
What we do is very specific: we convert resins such as PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys into a truly usable product; We also do modified PPO, PPS, and thermoplastic elastomers; We also handle nylon resin, sub-brand materials, and bulk materials from major chemical giants, and we also regularly collect nylon raw materials, sprue recycling, and various nylon scraps, with official disposal channels.
The additive system in the formula is tailored to the working conditions of each piece—regular additives are always in stock, special models are matched as needed; You specify the operating conditions and grade, and the materials and additives are all prepared in one go
