传感器壳体换料，栽跟头的地方往往不在雷达罩的透波上，而在那条焊缝上。
上个月，一家做智驾传感器壳体的客户把两套上下壳寄了过来，快递盒里垫了泡沫，两套件都用扎带捆着。
随件附了一张手写的纸条，只有一行字："同料同模，焊接后气密不稳。"
电话里他说得更直白："换料前焊一百个坏不了一个，换完这批，抽检线上下不来。"
我先问了他三句话。
"换的是基材，还是连玻纤含量一起换了？"
"焊接参数跟着新料重新摸过没有？"
"气密是在件刚下线测的，还是调湿以后测的？"
他想了半天，说头一句模糊，第二句没摸，第三句一直是下线就测。
这句话背后是传感器壳体换料最常见的一类误判：把焊接当成一道和材料无关的工序。
两分钟看懂：换料以后，焊缝为什么先出问题
塑料焊接不是把两块料"粘"起来，是让两边的分子链在界面重新缠在一起。
界面能不能缠上，取决于三件事：两边的熔体温度够不够、界面上有没有别的东西挡着、玻纤是不是都挤在了这里。
换料动了基材和玻纤含量，前两件事跟着变；换料动了润滑体系，第二件事直接出问题。
一句大白话：焊缝是两块料重新长在一起的地方，中间隔着东西就长不牢。
那条时间线，就是这批壳体的真实经过。
起点是换料后的第一批件：外观合格、装配顺畅、焊线漂亮，成本还比原来低了些，车间里松了口气。
潜伏期在第二个月。气密抽检开始偶发地报不合格，一个班次出一两个，按偶发处理，判给"焊接机参数波动"。
爆发在淋雨试验那一轮：整箱件里渗进去的比例明显上来，客户把这一批挂起，产线等料。
结算是追溯。焊缝剖面做下来，界面处有明显的助剂富集层，玻纤也堆在焊缝两侧，跟焊接机的稳定与否关系不大。
把"抽检一个班次出一两个"换算一下：一班 2000 件，看起来不良率不到千分之一，但一条焊线一年跑下来，这个比例就够让客户开质量会。
真正麻烦的不是不良率，是不良没有规律——今天这一模好，明天开一样的参数又不对。
一、换料前，这六个维度里四样要落到数字
传感器壳体件件不一样，工况要用温度、湿度与吸湿、振动、气密、外观与光学、电气六个维度问。
温度上，车外件夏天在阳光下的表温能到 85℃ 上下；激光雷达外壳如果带化冰加热，局部还要扛 60–80℃ 的加热段。
湿度这一维最容易被漏掉。壳体是吸湿材料，装到车上之后会慢慢吸到平衡状态，尺寸跟着变。
振动是第三维。传感器件装在保险杠内、后视镜附近、车顶这些位置，整车路谱都要过一遍。
气密是第四维，也是焊接质量的直接考题。常见口径是浸水或压力衰减法，泄漏率按客户企标卡。
外观与光学是第五维。毫米波雷达罩要透波，摄像头侧要遮光，激光雷达窗口要过特定波段。
电气是第六维。壳体上常有屏蔽、接地与静电耗散的要求，导电填料和屏蔽方案要一起谈。
把这几维里的数字先问齐：长期温度、吸湿后尺寸允差、泄漏率门限、屏蔽要求。
一个 120 毫米长的壳体，材料吸湿 0.6% 就是 0.72 毫米的尺寸变化——密封槽和卡扣的余量，很多就是这么被吃掉的。
二、四条路线摆开，不做谁更好的判断
| 路线 | 耐温与刚性 | 焊接友好度 | 吸湿与尺寸 | 常从哪条换过来 |
|---|
| PA6-GF30 | 中等，够用 | 宽，超声与热板都好做 | 吸湿偏高，长件尺寸要留量 | 通用工程塑料或金属件 |
| PA66-GF30 | 较高，发动机舱边件可用 | 较窄，对干燥与模温敏感 | 吸湿略低，需调湿后量 | PA6 强度不够的件 |
| 高温尼龙 PA6T 体系 | 高，回流与高温段可用 | 窄，窗口要重摸 | 吸水低，尺寸稳 | 高温位置的原金属件 |
| 矿物填充 PA6 | 刚性中等，各向异性小 | 好做，界面易熔合 | 吸湿最低，尺寸最稳 | 玻纤增强件 |
四条路线没有谁更好，只有哪条跟你现有的焊接线、模具和装配公差兜得住。
玻纤增强路线的代价集中在焊缝和吸湿尺寸两项：玻纤提高了本体刚性和耐温，但在焊缝处它不参与缠结，反而稀释了树脂的接触面积。
矿物填充路线反过来，尺寸和焊接都舒服，代价是刚性和耐热让出去一截。
高温尼龙路线的窗口最窄，换来的是耐温和低吸水，但焊接参数要从头摸一遍，不能照搬。
先把"为什么换"写清楚：是为了降本、为了耐温、还是为了供货稳定性，三条动机会导向不同的路线。
三、换料要重验的那张表
下面这张表把上面的约束落成可核对的动作。门限是方向性建议，不是验收标准，实际数值要由你的件和你的焊接线定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 换料后常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 焊接强度 | 不低于本体的七成 | 焊接样条拉伸，参考 ISO 527 | 焊缝开裂、暗分层 | 调焊接参数 + 平衡润滑体系 | 内外润滑平衡 |
| 气密性 | 按客户企标泄漏率门限 | 压力衰减法或浸水法 | 淋雨与浸水渗漏 | 加严焊缝熔深与保压 | — |
| 吸湿后尺寸 | 装配与密封槽仍在公差内 | 调湿后三坐标 | 卡扣错位、密封槽压不实 | 低吸水基材 + 调湿工艺 | — |
| 熔接线强度 | 按结构应力另定 | 短射取样 + 拉伸 | 沿熔接线开裂 | 挪浇口 + 提模温 | 内外润滑平衡 |
| 耐湿热老化 | 湿热循环后力学保持七成以上 | 双 85 或温湿循环 + ISO 527 | 长期泛黄、脆化 | 稳定化体系 | 抗氧剂 |
| 透波（雷达罩件） | 介电常数低且批次稳 | 介电常数与损耗角正切 | 探测距离波动 | 非导电体系，避碳纤 | — |
| 屏蔽与静电 | 按电磁与 ESD 要求 | 表面电阻与屏蔽效能 | 接地不良、静电累积 | 导电嵌件或本体导电体系 | — |
这张表怎么用：前两行是硬关。焊接强度和气密过不去，件在装配线上就下不来，后面几行没有必要谈。
第三行是换料最容易翻车的一项，因为它显形慢——件当天是合格的，装到整车上过了一个梅雨季才出问题。
第四行和第一行是一对。熔接线强度和焊接强度都是"界面的强度"，一个是注塑界面的，一个是二次连接的。
引用标准时把版本年份写进规格书。同一条拉伸曲线，试样形状不同，数就不同，两家比对之前先把方法对齐。
四、换料以后最常见的四种失效
失效一：焊缝开裂或暗分层。多数人的第一反应是"焊接机参数不对"，去反复调振幅、压力和时间。
调完以后有时候确实好了两天，但下一批又回来——说明问题的根不在设备上。
这一条要从助剂侧归因：润滑体系里外润滑过量，它会在熔体表面形成一层隔离，界面本来就靠熔体互相浸润，这层隔离等于在焊缝中间垫了一张膜。
内润滑不足是另一头：熔体粘度高，流动前沿在焊缝处汇合时温度已经掉下来，两边没能真正熔在一起。
所以焊接强度掉，先看润滑体系是不是内外失衡，再看焊接参数，最后才谈基材。
失效二：气密在调湿以后才不合格。根因不是焊缝，是尺寸——吸湿把壳体的配合面撑开了。
这类问题在下线检测里几乎发现不了，因为件那时候还是干的。
失效三：同一批件里，焊缝强度忽好忽坏。这不是"料不稳定"，常见是助剂分散不均匀，不同位置的界面状态就不一样。
失效四：雷达罩件换料后探测距离波动。根因往往是体系里混进了导电组分，或者壁厚精度跟着变了。
这里有一句我想说清楚：很多人换料以后焊不牢，第一件事是去调机器，其实有一半的账要算在料里的润滑剂上。
焊接焊的是塑料，不是润滑剂。界面上的东西越少，焊缝越可靠。
五、加工与验证，顺序不能换
栽在传感器壳体上的客户，多数不是没做验证，是顺序反了：先试模，再补材料数据，最后才发现焊接要重摸。
头一件事是干燥。吸水料含水超标，进料筒就被剪链，件表面出银纹、力学下降，而且显形很晚。
我们经手的换料投诉里，有一类特别典型：同一批料、同一个模具，这一模好下一模脆，配方一个字没改，是干燥。
第二件事是模温。模温低，玻纤被冻在表面形成浮纤；同时熔接线位置熔合变差，短射取样一测就看出来。
浮纤这件事客户经常判错方向。有人看到表面发白就要求"换个低玻纤的料"，把模温表一查，80℃。提到 115℃，同一批料同一个模具，表面基本就干净了。
第三件事是焊接参数。超声波焊接的振幅、压力、时间、熔深，要跟着新料重摸一遍，至少要跑三档对比。
如果是激光焊或热板焊，透光率、加热时间和压合方式也要重排。
第四件事是调湿。尼龙件装到车上会吸到平衡，量测条件要和客户一起定，是干态交货还是调湿后交货。
验证顺序建议这样排：
1. 材料级：含水率、干态与湿态力学保持率
2. 界面级：熔接线强度（短射取样）、焊接样条强度
3. 工艺窗口：不同模温与保压打出来的件做对比，焊接参数跑三档
4. 件级：调湿后尺寸与密封槽配合、气密复测
5. 整机级：装到传感器总成过环境耐久与整车抽检
前一项不通过就往下走，后面测出来的数没有解释意义。
为什么顺序不能换？因为焊接强度依赖界面状态，界面状态依赖模温与熔体温度，而熔体温度又依赖含水率。跳着走，得到的是一个只对那一模有效的结论。
六、边界：这几种情况，先别换
这一段可能比前面几段更值钱，因为它帮你在开工前止损。
其一，长期工作温度稳定在 150℃ 以上的位置。普通增强体系在这个区间长期表现的数据支撑不足，要看高温尼龙路线，或者留在金属上。
其二，密封面靠极窄公差压住、且要求干态装配的件。尼龙吸湿带来的尺寸变化压不住，这类要看金属或专门的低吸水体系。
其三，屏蔽效能要求很高、且不允许加导电嵌件的壳体。普通改性尼龙给不了这个效果，该走金属或导电涂层的组合方案。
其四，焊接方式还没定的件。超声、热板、激光对料的要求差很远，工艺不定先料，等于闭着眼跳。
把这四条写在前面，不是劝退，是省时间——样品顺、批量卡、整案回退，学费比一开始不换高得多。
七、换料风险清单
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 收缩率随玻纤含量变，长件要复算 | 只换料不核收缩，装不上 |
| 干燥 | 按实测含水率定窗口，除湿干燥机必备 | 热风干燥对吸水料基本无效 |
| 料温与模温 | 玻纤料窗口不同，浮纤靠模温压 | 照抄原件的温度档位 |
| 保压与脱模 | 脱模体系换低迁移型号，避免界面污染 | 沿用原脱模剂，焊缝变弱 |
| 焊接 | 振幅、压力、时间、熔深全部重摸 | 照搬原参数，气密不稳 |
| 调湿 | 强制调湿并称重判定，再复测尺寸 | 下线就量，数据不成立 |
| 气密 | 检测条件与判定口径与客户对齐 | 干态过、湿态不过 |
| 验证顺序 | 材料→界面→工艺→件级→整机 | 前一项未过就往下走 |
八、打样试模排程
给传感器壳体换料排试模，通常分三轮，轮次之间不跳步。
第一轮·小样比对：用你的原模具打 3–5 模，只验含水率、外观、短射件的熔接线位置和浮纤情况。这一轮不追性能，先把"料能不能填进去、界面长什么样"确认掉。
留样两件，标注批号与干燥参数，至少留到第二轮结束。
第二轮·界面与工艺：固定料，变模温与保压打两组对比件，同时把焊接参数跑三档。验熔接线强度、焊接样条强度、焊缝剖面。
这一轮基本决定量产参数和焊接档位。留样按批次封存，至少留到量产稳定后三个月。
第三轮·调湿与整机：按你的调湿口径处理，复测尺寸、密封槽配合与气密，然后装到传感器总成走环境耐久。
这一轮过了，才建议放量。留样封存覆盖首批量产，方便追因。
三轮的时间账要提前算：第一轮到第二轮通常两周，焊接参数如果要从头摸，会再占一周；第三轮看客户的整车排期，往往一个月以上。
想砍轮次可以，但砍掉的那一轮，通常会以"批量返工"的形式补回来。
九、几个被反复问到的问题
问：换料以后焊接参数一定要重摸吗？
答：要。超声与激光的窗口都跟熔体行为挂钩，换了基材和玻纤含量，原来的档位只是碰巧能用。
问：气密到底什么时候测？
答：按客户的实际服役状态测。件装到车上会吸湿，所以调湿后的数据才是可信的那一组。
问：能不能用导电填料解决屏蔽，顺便省掉嵌件？
答：看要求。导电填料会影响透波件的介电表现，也会改变焊接窗口，雷达罩这类件要单独评估。
问：批次一致性怎么做到？
答：关键牌号批批留样，含水率、灰分与力学随批出报告，任何一项漂移就整批挂起。做的是数据链，不是一张价目表。
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。
把料倒进机器之前，能和工艺一起定的，就先定下来。
基材、玻纤含量、干燥窗口、焊接方式这四样一旦定了，粒子只是把结论执行一遍。换料尤其如此：焊接参数和调湿口径不动，换谁来焊都不稳。
这类件的换料与试模，可以一起聊。
When replacing sensor housings, the stumbling point is often not on the radar cover's wave-transmitting area, but on that weld seam.
Last month, a customer who makes smart driving sensor housings sent over two sets of upper and lower shells. Foam was placed in the courier box, and both sets were tied with cable ties.
A handwritten note was attached, containing only one line: 'Same material, same mold, the airtightness is unstable after welding.'
On the phone he spoke more bluntly: 'Before changing the material, soldering a hundred pieces wouldn't ruin a single one; after changing this batch, random inspections on the production line couldn't keep up.'
I first asked him three questions.
Are you replacing just the substrate, or did you also change the fiberglass content along with it?
Have the welding parameters been re-checked with the new material?
Was the airtightness tested right after the part came off the line, or after adjusting the humidity?
He thought for a long time and said the first sentence was unclear, he didn't get the second sentence, and the third sentence was always offline when tested.
Behind this sentence is the most common type of misjudgment in sensor housing material replacement: treating welding as a process unrelated to the material.
Understand in Two Minutes: Why Welding Seams Fail First After Material Change
Plastic welding is not about 'sticking' two pieces of material together, but about allowing the molecular chains on both sides to re-entangle at the interface.
Whether the interface can bond depends on three things: whether the melt temperatures on both sides are sufficient, whether there is anything else blocking the interface, and whether all the glass fibers are squeezed here.
Changing the material affected the base material and glass fiber content, so the first two things changed accordingly; changing the material affected the lubrication system, and the second thing directly caused problems.
In plain words: a weld is the place where two pieces of material grow back together, and if there's something in between, it won't hold firmly.
That timeline is the true course of these shells.
The starting point was the first batch of parts after the material change: the appearance was acceptable, assembly was smooth, the welding was neat, and the cost was even lower than before, which brought a sigh of relief in the workshop.
The incubation period is in the second month. Random air-tightness inspections started occasionally reporting failures, with one or two per shift; they were treated as occasional incidents and attributed to 'welding machine parameter fluctuations'.
The outbreak occurred during that round of rain tests: the proportion of leakage into the whole box clearly increased, and the customer put this batch on hold while the production line waited for materials.
Settlement is retrospective. When the weld cross-section was examined, there was an obvious layer of additive enrichment at the interface, and the glass fibers were also stacked on both sides of the weld, which has little to do with the stability of the welding machine.
Convert 'randomly inspect one or two per shift': for a shift of 2,000 pieces, the defect rate seems to be less than one in a thousand, but over a year on a production line, this proportion is enough for the customer to hold a quality meeting.
The real problem is not the defect rate, but the unpredictability of the defects—today this batch is fine, but tomorrow using the same parameters, it goes wrong.
1. Before changing the material, four out of these six dimensions need to be quantified.
Sensor housing components are different, and operating conditions are evaluated across six dimensions: temperature, humidity and moisture absorption, vibration, airtightness, appearance and optics, and electrical conditions.
In terms of temperature, the surface temperature of exterior car parts can reach around 85℃ under sunlight in summer; if the lidar housing has ice-melting heating, some parts also have to withstand heating sections of 60–80℃.
The humidity dimension is the easiest to overlook. The casing is made of hygroscopic material, and after being installed in the car, it will slowly reach an equilibrium state, with its size changing accordingly.
Vibration is the third dimension. Sensors are installed in locations such as inside the bumper, near the rearview mirror, and on the roof, and the entire vehicle's road spectrum must be tested.
Air tightness is the fourth dimension, and it is also a direct test of welding quality. Common methods are water immersion or pressure decay, and the leakage rate is based on customer enterprise standards.
Appearance and optics are the fifth dimension. The millimeter-wave radar cover needs to be transparent to waves, the camera side needs to block light, and the lidar window needs to pass specific wavelengths.
Electricity is the sixth dimension. The enclosure often has requirements for shielding, grounding, and electrostatic dissipation, and conductive fillers and shielding solutions need to be discussed together.
First, ask for all the numbers in these dimensions: long-term temperature, dimensional tolerance after moisture absorption, leakage rate threshold, and shielding requirements.
A 120-millimeter-long casing, with the material absorbing 0.6% moisture, results in a dimensional change of 0.72 millimeters — the tolerances for the sealing grooves and clips are largely consumed this way.
2. Lay out the four routes without judging which one is better
| Route | Temperature Resistance and Rigidity | Weldability | Moisture Absorption and Dimensions | Which one do you usually switch from? |
|---|
| PA6-GF30 | Medium, enough | Wide, both ultrasound and hot plate are easy to do | High moisture absorption; allow extra length for long items | General engineering plastics or metal parts |
| PA66-GF30 | Higher, engine compartment side members are usable | Narrower, sensitive to drying and mold temperature | Moisture absorption is slightly low, requires adjustment of moisture before measurement | Parts with insufficient PA6 strength |
| High-temperature nylon PA6T system | High, suitable for reflux and high-temperature sections | Narrow, the window needs to be touched again | Low water absorption, stable dimensions | Original metal parts in high-temperature locations |
| Mineral-filled PA6 | Moderate rigidity, low anisotropy | Easy to use, interface easily integrates | Lowest moisture absorption, most stable dimensions | Glass fiber reinforced component |
None of the four routes is better; it’s just a matter of which one can accommodate your existing welding line, molds, and assembly tolerances.
The cost of the glass fiber reinforced route is concentrated on welds and moisture absorption dimensions: glass fiber increases the bulk rigidity and temperature resistance, but at the weld it does not participate in entanglement, instead diluting the resin's contact area.
The mineral-filled route is reversed, the size and welding are comfortable, but the cost is sacrificing some rigidity and heat resistance.
The window for the high-temperature nylon route is the narrowest, which brings heat resistance and low water absorption, but the welding parameters need to be figured out from scratch and cannot be copied directly.
First, clearly write down 'why it is being changed': is it to reduce costs, to improve temperature resistance, or to ensure supply stability? The three motivations will guide different paths.
3. The form that needs to be re-checked when changing materials
The table below translates the above constraints into actionable steps that can be checked. The thresholds are directional suggestions, not acceptance criteria; the actual values should be determined by your parts and your welding line.
| Indicator | Directional threshold | Verification Method / Standard | Common failures after material change | Common solution | Corresponding auxiliary agent system |
|---|
| Welding strength | Not less than seventy percent of the main body | Welded spline tension, refer to ISO 527 | Weld cracking and subsurface lamination | Adjust welding parameters Balance lubrication system | Internal and external lubrication balance |
| Air tightness | According to the customer's standard leakage rate threshold | Pressure decay method or immersion method | Rain Exposure and Water Leakage | Increase weld penetration and hold pressure | — |
| Dimensions after moisture absorption | Assembly and sealing groove are still within tolerance | Coordinate measuring after humidity adjustment | Misaligned buckle, sealing groove not properly pressed | Low water-absorption substrate Humidity control process | — |
| Weld line strength | Determine separately according to structural stress | Short shot sampling Stretching | Cracking along the weld line | Pouring spout Form release temperature | Internal and external lubrication balance |
| Damp heat aging | After the wet-heat cycle, mechanical strength remains above 70% | Double 85 or temperature-humidity cycle ISO 527 | Long-term yellowing and brittleness | Stabilization system | Antioxidant |
| Radar-transparent (radome) | Low dielectric constant and stable from batch to batch | Dielectric constant and loss tangent | Detection distance fluctuation | Non-conductive system, avoid carbon fiber | — |
| Shielding and Static Electricity | According to electromagnetic and ESD requirements | Surface Resistance and Shielding Effectiveness | Poor grounding, static accumulation | Conductive insert or body conductive system | — |
How to use this table: The first two rows are tough levels. If the welding strength and airtightness fail, the part won't come down on the assembly line. The following rows are not necessary to discuss.
The third line is the easiest place for material changes to go wrong because it manifests slowly — a part may meet standards on the day it is made, but problems only appear after being installed on the vehicle and going through a rainy season.
The fourth row and the first row are a pair. Both the weld line strength and the bonding strength are "interface strengths": one is the injection molding interface, and the other is the secondary connection.
When citing standards, include the version year in the specifications. For the same tensile curve, the numbers differ if the specimen shapes are different, so both parties should align the methods before comparison.
4. The Four Most Common Failures After Material Replacement
Failure 1: Weld cracking or hidden delamination. Most people's first reaction is 'the welding machine parameters are incorrect,' leading them to repeatedly adjust the amplitude, pressure, and time.
Sometimes after adjustment, it does improve for two days, but the next batch comes back—this shows the problem isn't with the equipment.
This point should be attributed to the additives side: if there is excessive internal and external lubrication in the lubrication system, it will form a layer of isolation on the surface of the melt. The interface originally relies on the melt mutually wetting each other, so this layer of isolation is equivalent to placing a film in the middle of the weld.
Insufficient internal lubrication is another issue: the melt viscosity is high, and by the time the flow fronts meet at the weld, the temperature has already dropped, so the two sides do not truly fuse together.
So when welding strength drops, first check whether the lubrication system is imbalanced, then look at the welding parameters, and only finally discuss the substrate.
Failure 2: The airtightness becomes non-compliant only after humidity adjustment. The root cause is not the weld, but the dimensions — moisture absorption has expanded the mating surfaces of the housing.
This kind of problem is almost impossible to detect in offline inspections because the parts are still dry at that time.
Failure three: In the same batch, the weld strength fluctuates. This is not due to 'unstable materials'; it is commonly caused by uneven dispersion of additives, resulting in different interfacial conditions at different positions.
Failure 4: After replacing radar dome components, the detection range fluctuates. The root cause is often that conductive components have mixed into the system, or the wall thickness precision has changed accordingly.
There is one thing I want to make clear: when many people find that soldering doesn't hold after changing materials, the first thing they do is adjust the machine. In fact, half of the issue should be attributed to the lubricant in the material.
Welding welds the plastic, not the lubricant. The less there is on the interface, the more reliable the weld.
5. Processing and verification, the order cannot be changed
Most of the customers who failed with the sensor housing didn't skip verification; they just did things in the wrong order: first trial molding, then supplementing material data, and only in the end did they realize the welding needed to be redone.
The first thing is drying. When the water-absorbing material exceeds the moisture limit, the feed barrel gets chain-cut, silver streaks appear on the surface of the part, mechanical properties decline, and the defect becomes visible very late.
Among the material change complaints we handle, there is a particularly typical type: the same batch of material, the same mold—one mold comes out fine while the next one is fragile, with the formula not changed a bit; it's the drying.
The second thing is mold temperature. If the mold temperature is low, the glass fibers get frozen on the surface, forming floating fibers; at the same time, the weld line fusion worsens, which can be seen immediately during short-shot sampling.
Customers often judge the direction of floating fibers incorrectly. Some see the surface turning white and request 'to switch to a lower glass fiber material.' When the mold temperature is checked, it's 80°C. Raising it to 115°C, for the same batch of material and the same mold, the surface is basically clean.
The third thing is welding parameters. The amplitude, pressure, time, and melt depth of ultrasonic welding need to be rechecked with new material, and at least three levels should be compared.
If it is laser welding or hot plate welding, the light transmittance, heating time, and bonding method also need to be rearranged.
The fourth thing is humidity adjustment. When nylon parts are loaded onto the vehicle, they will absorb moisture. The measurement conditions need to be determined together with the customer, whether to deliver in a dry state or after humidity adjustment.
It is recommended to arrange the verification sequence in this way:
1. Material level: moisture content, mechanical retention in dry and wet states
2. Interface level: Weld line strength (short shot sampling), weld spline strength
3. Process window: Compare parts produced with different mold temperatures and holding pressures, and run the welding parameters in three levels.
4. Part level: Fit with the sealing groove after humidity adjustment, re-test for airtightness
5. Complete machine level: Install into the sensor assembly for environmental endurance testing and vehicle random inspection
If the previous item fails, just move on; the numbers measured afterwards have no explanatory significance.
Why can't the order be changed? Because the welding strength depends on the interface condition, the interface condition depends on the mold temperature and the melt temperature, and the melt temperature depends on the moisture content. Skipping steps results in a conclusion that is only valid for that particular mold.
6. Boundaries: In these situations, don't change them for now
This section may be more valuable than the previous few sections because it helps you cut losses before starting work.
First, the long-term working temperature remains stable above 150°C. Ordinary reinforced systems lack sufficient long-term performance data in this range, so one should consider high-temperature nylon options or stick with metals.
Secondly, parts whose sealing surfaces are pressed together with extremely tight tolerances and require dry assembly. Nylon's dimensional changes due to moisture absorption prevent proper pressing; for these, you need to consider metals or specialized low-moisture-absorption systems.
Third, the enclosure requires high shielding performance and does not allow the addition of conductive inserts. Ordinary modified nylon cannot achieve this effect, so a combination of metal or conductive coating should be used.
Fourth, parts for which the welding method has not yet been determined. Ultrasonic, hot plate, and laser have very different material requirements. Deciding on the material before the process is set is like jumping blindly.
Writing these four points first is not to discourage you, but to save time — sample approval, batch hold, full case return; tuition is much higher if you don’t make changes from the beginning.
7. Material Replacement Risk List
| link; segment; part | What needs to be moved? | Points that are easy to overlook |
|---|
| Mold | The shrinkage rate changes with the glass fiber content, and long parts need to be recalculated. | Only replacing the material without verifying shrinkage, cannot install |
| Dry | Set the window according to the actual measured moisture content; a dehumidifying dryer is essential. | Hot air drying is basically ineffective for water-absorbing materials |
| Material Temperature and Mold Temperature | Different fiberglass materials require different window settings, with floating fibers relying on mold temperature and pressure. | Copy the original temperature setting |
| Pressure Holding and Demolding | Switch to a low-migration grade in the demolding system to avoid interface contamination | Continuing to use the original release agent, the weld becomes weaker |
| Welding | Amplitude, pressure, time, and melt depth all need to be redone | Copying the original parameters, the airtightness is unstable |
| Humidity control | Forced moisture adjustment and weight determination, then re-measure the dimensions | Offline is just quantity; the data is invalid |
| Airtight | Testing conditions and evaluation criteria aligned with the customer | Passes when dry, fails when wet |
| Verification order | Material → Interface → Process → Component Level → Complete Machine | If the previous item fails, just move on. |
8. Proofing and Trial Molding Schedule
Changing the material and trial molding for the sensor housing is usually done in three rounds, without skipping steps between rounds.
First round · Sample comparison: Use your original mold to make 3–5 samples, only checking moisture content, appearance, the weld line position of short-shot parts, and floating fibers. This round does not pursue performance; first, confirm whether the material can fill the mold and what the interface looks like.
Keep two samples, mark the batch number and drying parameters, and keep them at least until the end of the second round.
Second round · Interface and process: Fix the material, vary the mold temperature and holding pressure to create two sets of comparison pieces, while running the welding parameters in three levels. Test the strength of the fusion line, the strength of the welded spline, and the weld cross-section.
This round basically determines the mass production parameters and welding settings. Samples are to be sealed by batch and kept for at least three months after mass production stabilizes.
Third round: Humidity adjustment and complete machine: Handle according to your humidity adjustment specifications, re-measure dimensions, fit of sealing groove and airtightness, then install into the sensor assembly for environmental durability testing.
Only after this round passes is it recommended to increase the volume. Keep samples sealed to cover the first batch of mass production, making it easy to track the cause.
The timing for the three rounds needs to be calculated in advance: the first to the second round usually takes two weeks, and if the welding parameters need to be tested from scratch, it will take another week; the third round depends on the customer's whole vehicle schedule, often more than a month.
You can cut rounds, but the rounds that are cut are usually made up later in the form of 'batch rework'.
9. Several Frequently Asked Questions
Question: Do the welding parameters have to be recalibrated after changing the material?
Answer: Yes. The windows for ultrasound and laser are both linked to the behavior of the melt. Changing the substrate and fiberglass content means the original settings only happened to work.
Question: When exactly should the airtightness be tested?
Answer: Measure according to the customer's actual service condition. The parts will absorb moisture once installed on the vehicle, so the data after humidity adjustment is the reliable set.
Question: Can conductive fillers be used to achieve shielding, and at the same time eliminate the need for inserts?
Answer: It depends on the requirements. Conductive fillers can affect the dielectric performance of wave-transmitting components and can also change the welding window. Parts like radomes need to be evaluated separately.
Question: How is batch consistency achieved?
Answer: Samples are kept from each batch of key grades, and reports are issued for each batch regarding moisture content, ash content, and mechanical properties. If any one of these items deviates, the entire batch is suspended. What we are doing is a data chain, not a price list.
The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the materials and auxiliaries are prepared together at once.
Before pouring the material into the machine, agree on what can be decided together with the process first.
Once the substrate, fiberglass content, drying window, and welding method are set, the particles just execute the conclusion. This is especially true when changing materials: if the welding parameters and humidity adjustment aperture remain the same, no matter who does the welding, it won’t be stable.
The material replacement and mold trial for this type of part can be discussed together.
