门锁、摇窗器、雨刮器、座椅调节——汽车上的小模数齿轮，是尼龙件里用量最大、也最"不起眼"的一类。
正因为不起眼，它的选材常被当成"随便挑个增强尼龙就行"。
但这一类件的失效率，在实际项目里并不低。
门锁和摇窗器里的齿轮，个头小到不起眼。
模数一点零以下，齿宽几毫米，一只手里能摊开七八个。
但整车厂对它的要求一点不低：全寿命几万次动作，一次卡顿就算售后。
一家做摇窗器的工厂算过账，齿轮断齿的售后成本是齿轮本身价格的几十倍。
小件的价值不在价格上，在整个机构的可靠性里。
一、小模数齿轮和大齿轮是两回事
先把两者的要求并排放：
| 维度 | 小模数齿轮 | 大模数齿轮 |
|---|
| 传递扭矩 | 低 | 中高 |
| 转速 | 高 | 中低 |
| 关键失效 | 磨损、断齿、尺寸漂移 | 齿根疲劳、点蚀 |
| 首要指标 | 尺寸稳定 + 韧性 | 承载能力 |
| 玻纤含量 | 低到中（GF15-30） | 中高（GF30-50） |
| 加工难点 | 一模多穴的一致性 | 齿面精度与冷却 |
差别最大的一行是"关键失效"。
大齿轮怕的是疲劳，小齿轮怕的是尺寸漂移和脆断。
所以小齿轮的选料重点，从"承载"挪到了"稳定"。
二、小齿轮的三个特点
特点一：扭矩低。 门锁、摇窗器这类机构，传递的扭矩通常在很小的量级。所以不需要高玻纤来撑刚性。
特点二：转速高、循环次数多。 雨刮器、摇窗器都是反复启停的机构，循环次数可以很高。所以耐磨和自润滑比承载重要。
特点三：尺寸小、精度要求高。 齿轮小，同样的尺寸偏差带来的相对误差更大。所以抗吸湿变形、抗成型收缩，是这类件的核心诉求。
三个特点指向同一个结论：小模数齿轮要的是"稳"，不是"强"。
三、选料方向与一个容易忽略的工艺前提
小模数齿轮的主流方向是 PA6 或 PA66 加中等玻纤（GF15-30），配耐磨自润滑体系（如二硫化钼、硅油体系）。
为什么不用高玻纤？因为高玻纤会带来两个坏处：各向异性放大（小齿轮对这一点更敏感），以及熔接线强度下降（小齿轮的浇口安排往往受限，熔接线位置难以避开）。
但这里有个比选料更常见的问题：
"一批脆、一批不脆"，在塑料齿轮上首先查干燥，不是先查配方。
尼龙（尤其 PA66）含水率超标时，熔融过程中会发生水解降解，分子链断裂，出来的件就是脆的。而这个现象在不同批次之间表现得很随机——同一批料、同一台机，只要干燥状态不同，结果就不同。
尼龙用普通热风干燥往往等于没干燥充分，这一点在齿轮件上后果尤其明显：齿轮是薄壁小件，任何一点降解都会直接体现在齿根强度上。
先排除工艺因素，再谈换料，顺序不能反。
四、一模多穴带来的一致性挑战
小齿轮尺寸小，为了效率通常是一模多穴。
这就带来一个特有的问题：穴与穴之间的差异。
穴间差异的来源有几个：
流道长度不同，充填压力与速度不同
各穴冷却条件不同（靠近冷却水路的穴凉得更快）
保压传递不均，收缩率不一致
结果是同一模出来的齿轮，尺寸可能落在不同的公差带里。
对齿轮来说，尺寸差异直接影响啮合间隙——一个模次里的差异，比材料本身的差异更常见。
所以这类件要特别关注：流道平衡设计、模温均匀性、以及是否需要对不同穴分别标定尺寸。
五、三个常见坑
坑 1：用高玻纤换取"更保险"。
小齿轮本来扭矩低，上 GF50 只会让熔接线更脆、各向异性更强，得不偿失。
坑 2：忽略吸湿后的尺寸漂移。
齿轮装车前尺寸合格，跑一段时间后间隙变了——这往往是吸湿导致，不是磨损导致。后处理调湿能提前把这一步做完。
坑 3：把浇口放在齿面上。
浇口位置决定了熔接线位置。熔接线落在受力齿面上，等于给断裂预埋了起点。 这一条属于模具设计，但选料时就应该一起讨论。
六、验证清单
1. 尺寸稳定性试验（成型后立即测 + 吸湿平衡后复测）
2. 齿根强度试验（重点测熔接线位置）
3. 耐久循环试验（按实际机构循环次数）
4. 低温冲击试验（冬季工况）
5. 多穴一致性抽检（每个穴都要抽）
第 5 条是小模数齿轮特有的一项，很多项目会漏。
另外建议加一项装配后的整机噪音测试。小模数齿轮的异响，往往在整机装配后才暴露——单件测试测不出来，因为噪音来自齿轮与对偶件的配合，不只来自齿轮本身。
验收标准也要写清"在什么状态下测"：成型后立即测，还是调湿平衡后测。同一个齿轮，两个状态下能差出好几个丝，直接影响啮合间隙。
小模数齿轮对材料的要求，集中在两点：齿形保持和耐磨。
模数小，齿就薄，轮齿根部能用上的截面很小，对强度极其敏感。
含油改性的牌号在无润滑的摇窗器机构里表现更好，摩擦系数低且稳定。
玻纤在这类件里要谨慎，玻纤会让齿面磨出犁沟，还会磨轴。
不少工厂吃过这个亏：加玻纤提强度，齿面是硬了，配对的金属轴却先磨坏了。
小模数齿轮的选型，看的不是单件强度，是摩擦副两边的寿命配平。
追问一：含油 POM 和 PA66 在小模数齿轮上怎么分？
看润滑状态和负载。无油润滑、中低负载的摇窗器和门锁机构，含油 POM 是主流，摩擦稳、噪音低。负载冲击大的位置，比如锁块联动件，PA66 加增韧更抗打。两个都过不了的位置，考虑 POM 加 PTFE 或者上金属。
追问二：模数小到什么程度该回头用金属？
经验线在模数零点五附近。再往下，齿根截面太薄，塑料的强度裕量放不下加工误差和装配误差。硬要用塑料的，得靠金属嵌件齿圈这类复合结构，成本和复杂度都上去了，通常不划算。
一单断齿的追查
某摇窗器齿轮冬季集中断齿，齿根断口整齐。排查发现断齿和低温冲击有关：试验规范按常温装配、低温运行做的，漏了低温装配工况。东北冬季产线零下装配，齿轮内圈被压出一圈预应力，运行几天后从应力集中点开裂。补低温装配试验后，同类投诉归零。
小模数齿轮验收三查
查齿形（投影仪比对齿廓）、查配副（与轴和配合齿轮的磨损对检）、查低温（零下四十度冲击后齿根无裂）。三条写进进料检验，断齿类投诉能拦下一大半。
小模数齿轮还有个容易忽视的变量：注塑精度。
模数一点零的齿轮，齿形误差要控制在几个丝以内。
普通注塑能做到，但要把模具、工艺、材料收缩数据一起管起来。
材料换牌号，收缩率变了，齿形就跟着变，哪怕模具一副没动。
所以小模数齿轮的换料，视同换模具来验证。
一家门锁厂的做法值得参考：换料必做齿形投影比对，数据和老料叠图。
叠图上差异超过线的，直接判定不适合，不抱侥幸。
三个延伸问题
齿轮和轴的配合用什么公差？按塑料的蠕变量放大间隙，常温装配后跑合几天再复测。
噪声要求和材料有什么关系？含油和弹性体改性都能降噪，但降噪牌号的强度通常低一档，要配平。
小齿轮要不要做盐雾？门锁件在门腔内，盐雾间接接触，按整车厂规范大多要测。
定点资料清单
齿形投影叠图、配副磨损对检、低温装配与运行数据、含油量与摩擦系数报告。
四份资料是这一类件的标配，缺一份后期就多一轮扯皮。
小模数齿轮的供应链还有一层：一致性。
这类件单件价值低、用量大，供应商的批次一致性比牌号本身重要。
同一副模具、同一批料，不同时段打的齿轮齿形会漂。
漂移的来源是模温、保压、料筒状态这些工艺变量。
成熟供应商会把这些变量做成点检表，班班记录。
采购评审时看两样东西：点检表的填写质量和齿形叠图的留存习惯。
细节习惯比资质证书更能说明一家工厂的真实水平。
最后一组追问
齿轮件要不要留样？要，按批留样三年，断齿纠纷时能直接比对。
小齿轮的包装有讲究吗？有，散装磕碰伤齿，建议吸塑盘分层。
换供应商时要重新验证什么？齿形叠图、配副对检、低温冲击三样都要重做，牌号相同不等于工艺相同。
小件的管理逻辑一句话：用量越大，越要当成大件管。
小模数齿轮这一类，最后总结成一个采购视角。
它的采购难度不在议价，在信息。
齿形、含油率、配副状态，这些关键信息采购方往往拿不到全貌。
成熟的采购做法是把关键数据写进供货协议，要求随批提供。
协议里有了数据条款，供应商的一致性投入就有了回报通道。
数据随货走，是小件采购升级的分水岭。
收官三点
小件大管，是这类件全部管理的浓缩。
牌号是起点，批次一致性才是终点。
把看不见的参数变成看得见的条款，是采购真正的专业所在。
锁块、卡板这些件要求抗冲击和耐磨兼得，增韧 PA 系是主流。
锁块的失效模式是磨损后间隙变大，解锁力漂移。
因此锁块件的验证里有一项行程力曲线衰减测试。
曲线稳定，门锁的手感十年不变。
手感这类软指标背后，全是硬数据在撑。
这一篇的完整知识地图
模数定工艺路线，润滑状态定材料家族，配副对检定摩擦平衡，低温装配定试验边界，齿形叠图定批次验收。
五个定字连起来，就是小模数齿轮的全部选型逻辑。
断齿投诉最多的工厂，往往是五步里跳步最多的工厂。
把这一页逻辑贴在项目室的墙上，比任何培训都管用。
小模数齿轮教会行业的道理很朴素：越小的件，越没有小事。
门锁件还有法规层面的要求要说。门锁系统是安全件，有专门的强检规范，塑料齿轮所在的开闭机构要随总成一起过循环耐久。循环次数以万计，塑料件的老化和磨损在长循环里叠加出现。所以门锁齿轮的选型验证，从来不是单件测试，是随总成跑全寿命循环。供应商要能提供长循环的配套数据，只给单件物性表的方案在评审里走不远。这一条经验，几乎所有安全件都适用。
再补一个批次追踪的细节：齿轮件建议做日期码或者批次码注塑标识。断齿投诉回来，扫码就能锁定生产时段的工艺参数和材料批次。一家门锁厂靠这个习惯，把一次断齿投诉的追查从两周压缩到一天。客户对响应速度的感知，往往比对故障本身的感知更影响合作关系。小件配追溯码，成本几乎为零，回报却是信任级别的。
结语
小模数齿轮的选材判断链：
先定"稳"字优先（尺寸与批次一致性）→ 选中低玻纤 + 耐磨体系 → 再管住干燥与多穴一致性。
如果你手上有个小齿轮件在定料，把三样东西发过来：传递扭矩、循环次数要求、装配尺寸公差。
Door locks, window rollers, wipers, seat adjustments—small module gears on cars are the most widely used and also the most "inconspicuous" type of nylon component.
Because they are inconspicuous, their materials are often treated as "just pick any reinforced nylon and you'll be fine."
But the failure rate of these types of parts is not low in actual projects.
The gears in door locks and window shakers are so small they are almost inconspicuous.
Module below 1.0, a few millimeters wide, and you can open seven or eight in one hand.
But automakers have high demands for them: a full lifespan of tens of thousands of operations, and one lag counts as after-sales service.
A window shaker factory did the math: the after-sales cost of broken gears is dozens of times the price of the gear itself.
The value of small parts isn't in price, but in the reliability of the entire mechanism.
1. Small module gears and large gear are two different things
First, put the requirements for both side by side:
| Dimension | Small module gear | High module gear |
|---|
| Torque transmission | Low | Mid-high |
| Speed | High | Medium-low |
| Key failures | Wear, tooth breakage, dimensional drift | Tooth root fatigue, pitting |
| Primary indicators | Dimensional stability + toughness | Load-bearing capacity |
| Fiberglass content | Low to medium (GF15-30) | Medium-high (GF30-50) |
| Machining difficulties | Consistency of multiple cavities in one mold | Tooth surface accuracy versus cooling |
The biggest difference is "critical failure".
Large gears fear fatigue, while small gears fear dimensional drift and brittleness.
Therefore, the focus of small gear material selection has shifted from "load-bearing" to "stability."
2. Three characteristics of pinion gears
Characteristic one: Low torque. Mechanisms like door locks and window shakers usually transmit torque on a very small scale. Therefore, high fiberglass is not needed to support rigidity.
Feature two: high rotational speed and many cycles. Wipers and window shakers are mechanisms that start and stop repeatedly, with very high cycle counts. Therefore, wear resistance and self-lubrication are more important than load capacity.
Feature three: small size and high precision requirements. Small gears result in larger relative errors due to the same dimensional deviation. Therefore, resistance to moisture absorption, deformation, and molding shrinkage are the core requirements for these components.
Three characteristics point to the same conclusion: Small module gears require "stability," not "strength."
3. Material Selection Direction and an Easily Overlooked Process Premise
The mainstream direction for small module gears is PA6 or PA66 plus medium glass fiber (GF15-30), paired with wear-resistant self-lubricating systems (such as molybdenum disulfide and silicone oil systems).
Why not use high-grade glass fiber? Because high fiberglass brings two drawbacks: amplification of anisotropy (pinion is more sensitive to this), and reduced strength of the fusion line (pinion gate arrangement is often limited, making it hard to avoid the welding line position).
But there is a more common issue here than material selection:
"One batch is brittle, some is not." On plastic gears, the first check is dryness, not the formula.
When nylon (especially PA66) has excessive moisture content, hydrolytic degradation occurs during melting, molecular chains break, and the resulting parts become brittle. This phenomenon varies between batches—the same batch of material, same machine, as long as the drying state differs, the results will differ.
Nylon dried with ordinary hot air often means incomplete drying, which is especially obvious for gear parts: gears are thin-walled small parts, and any slight degradation directly affects the tooth root strength.
First, rule out process factors, then discuss material replacement; the order cannot be reversed.
4. Consistency challenges brought by multiple cavities in one mold
Small gears are small, so for efficiency, they usually have multiple cavities in one mold.
This brings a unique problem: differences between cavities.
There are several sources of inter-hole differences:
Different runner lengths, different filling pressure and speed
Different cavity cooling conditions (cavities near the cooling channel cool faster)
Uneven pressure transfer and inconsistent shrinkage rates
The result is gears produced from the same die, and their dimensions may fall within different tolerance zones.
For gears, size differences directly affect the meshing clearance—differences within a single die are more common than differences in the material itself.
Therefore, special attention should be paid to such parts: channel balance design, mold temperature uniformity, and whether dimensioning is needed for different cavities.
V. Three Common Pitfalls
Pit 1: Trading high fiberglass for "more safety."
Small gears have low torque; using GF50 only makes the fusion line more brittle and more anisotropic, which is not worth the risk.
Pit 2: Ignore dimensional drift after moisture absorption.
The gear size is qualified before installation, but after running for a while, the clearance changes—this is usually caused by moisture absorption, not wear. Post-treatment humidity control can complete this step earlier.
Plot 3: Place the gate on the gear surface.
The gate position determines the welding line position. The weld line falls on the load-bearing tooth surface, effectively embedding the starting point for the fracture. This belongs to mold design, but should be discussed together during material selection.
6. Verification Checklist
1. Dimensional stability test (test immediately after forming + retest after moisture absorption balance)
2. Tooth root strength test (focus on welding line position)
3. Durability cycle test (based on actual mechanical cycle count)
4. Low-temperature impact test (winter operation)
5. Multi-cavity consistency sampling inspection (each cavity must be sampled)
Item 5 is a unique item for small module gears, and many items may be missed.
Additionally, I suggest adding a complete machine noise test after assembly. Abnormal noises from small module gears often only become apparent after assembly—single-component testing can't detect them, because the noise comes from the coordination between the gear and the pairing part, not just from the gear itself.
Acceptance criteria should also specify "under what conditions": test immediately after forming, or after humidity adjustment and balance. For the same gear, several wires can differ between two states, directly affecting the meshing clearance.
Small module gears have material requirements focused on two points: tooth profile retention and wear resistance.
Low module means thin teeth, and the cross-section at the tooth root is very small and extremely sensitive to strength.
Oil-modified grades perform better in non-lubricated window shaker mechanisms, with a low and stable friction coefficient.
Be cautious with fiberglass in such parts, as it can cause the tooth surface to grind into grooves and also the shaft.
Many factories have suffered this disadvantage: adding fiberglass to increase strength hardens the gear surface, but the paired metal shaft wears out first.
When selecting small module gears, it's not about individual strength but about the lifespan and balance of both friction pairs
Follow-up Question 1: How do you differentiate between oil-containing POM and PA66 on small module gears?
Check the lubrication condition and load. For window regulators and door lock mechanisms with oil-free lubrication and medium to low loads, oil-containing POM is mainstream, providing stable friction and low noise. For positions with high load impacts, such as lock block linkages, PA66 reinforced for toughness is more impact-resistant. For locations where neither material suffices, consider POM with PTFE or adding metal.
Follow-up Question 2: At what small modulus should one go back to using metal?
The experience curve is around a modulus of 0.5. Going any lower, the tooth root cross-section becomes too thin, and the strength margin of the plastic cannot accommodate machining and assembly errors. If you insist on using plastic, you have to rely on composite structures like metal-inserted gear rings, which increases both cost and complexity, and is usually not worth it.
A case of a broken tooth investigation
A certain window regulator gear experienced concentrated tooth breakage in winter, with fracture surfaces at the tooth roots appearing neat. Investigation found that the broken teeth were related to low-temperature impact: testing standards were conducted with assembly at normal temperature and operation at low temperature, but the low-temperature assembly condition was missed. On a production line in Northeast China, assembly occurs below zero in winter, causing a ring of residual stress to be pressed into the inner circle of the gear, which then cracks at the stress concentration point after a few days of operation. After supplementing tests for low-temperature assembly, similar complaints dropped to zero.
Three Inspections for Small Module Gear Acceptance
Check tooth profile (compare tooth contour with a projector), check mating parts (inspect against wear with shafts and mating gears), check low temperature (no cracks at the tooth root after impact at minus forty degrees). These three items should be included in the incoming inspection, which can prevent more than half of the broken tooth complaints.
Small module gears have another easily overlooked variable: injection molding accuracy.
For a gear with a module of 1.0, the tooth profile error must be controlled within a few microns.
Ordinary injection molding can accomplish it, but you need to manage the mold, process, and material shrinkage data together.
When the material grade changes, the shrinkage rate changes, and the tooth profile changes accordingly, even if the mold hasn't been altered at all.
Therefore, the material change for small module gears is considered the same as changing the mold for verification.
The approach of a door lock factory is worth referring to: whenever materials are changed, a gear profile projection comparison must be done, and the data should be overlaid with the old material.
If the differences on the overlay exceed the line, it is directly judged as unsuitable, without taking chances.
Three extended questions
What tolerance is used for the fit between gears and shafts? Increase the clearance according to the creep of the plastic, and reinstall after a few days of running at room temperature before re-measuring.
What is the relationship between noise requirements and materials? Both oil-containing and elastomer-modified materials can reduce noise, but noise-reducing grades usually have one level lower strength, so they need to be balanced.
Should the small gears undergo salt spray testing? The door lock components are inside the door cavity, and the salt spray contact is indirect. According to most complete vehicle manufacturer specifications, testing is generally required.
Fixed-point data list
Tooth profile projection overlay, check for mating wear, low-temperature assembly and operational data, oil content and friction coefficient report.
Four pieces of documentation are the standard for this type of case; if one is missing, there will be another round of wrangling later.
There is another layer in the supply chain of small module gears: consistency.
These types of parts have low unit value and are used in large quantities, so the batch consistency of the supplier is more important than the grade itself.
Using the same mold and the same batch of material, the gear tooth profile can vary when produced at different times.
The source of the drift is process variables such as mold temperature, holding pressure, and barrel conditions.
Mature suppliers will turn these variables into a checklist and record them every shift.
When reviewing procurement, look at two things: the quality of the checklist completion and the habit of retaining gear profile overlays.
Attention to small habits can reveal a factory's true level better than qualification certificates.
The last set of follow-up questions
Should I keep samples of gear parts? Yes, I will keep samples for three years according to the batch, so that in case of broken teeth, they can be directly compared.
Is there any particular way to package small gears? Yes, if they are loose, they can get their teeth damaged from bumps, so it is recommended to use a blister tray with layers.
What needs to be re-verified when changing suppliers? The three items—tooth profile overlay, mating pair inspection, and low-temperature impact—all need to be redone. The same grade does not mean the process is the same.
The management logic for small items in one sentence: the greater the usage, the more they should be treated as large items.
For this category of small module gears, it is finally summarized from a purchasing perspective.
The difficulty in procuring it lies not in bargaining, but in information.
Tooth profile, oil content, and matching status—these key pieces of information are often not fully available to buyers.
A mature procurement practice is to write key data into the supply agreement and require it to be provided with each batch.
With data clauses in the agreement, the supplier's consistent contributions have a channel for returns.
Data follows the goods, marking a watershed in the upgrade of small-item procurement.
Three points to close
Small parts, big management, is the essence of managing all such parts.
The brand is the starting point, but batch consistency is the ultimate goal.
Turning invisible parameters into visible terms is where true professionalism in procurement lies.
For parts like lock blocks and pallets, both impact resistance and wear resistance are required, and toughened PA grades are the mainstream.
The failure mode of the lock block is that after wear, the clearance increases and the unlocking force drifts.
Therefore, in the verification of the lock block, there is a travel force curve decay test.
The curve is stable, and the feel of the door lock remains unchanged for ten years.
Behind tactile, soft indicators, it's all supported by hard data.
The complete knowledge map of this article
The modulus determines the process route, the lubrication state determines the material family, the mating pair determines the friction balance, low-temperature assembly determines the test boundaries, and the tooth profile overlay determines batch acceptance.
The five 'fixed' characters combined represent the entire selection logic for small module gears.
The factories with the most broken tooth complaints are often the ones that skip the most steps in the five-step process.
Posting this page of logic on the wall of the project room is more effective than any training.
The small-module gear teaches the industry a very simple truth: the smaller the part, the less trivial the matter.
There are also regulatory requirements for door lock components. The door lock system is a safety component and has specific mandatory inspection standards. The opening and closing mechanism, where the plastic gears are located, must undergo durability cycles along with the entire assembly. The number of cycles is in the tens of thousands, and the aging and wear of the plastic parts accumulate over long cycles. Therefore, the selection and verification of door lock gears has never been based on testing individual parts alone; it is always done by running the full assembly through its entire life cycle. Suppliers need to provide long-cycle supporting data; solutions that only provide individual material property sheets will not get far in the review. This experience applies to almost all safety components.
Adding another detail about batch tracking: It is recommended that gear parts have date codes or batch code injection markings. When a tooth break complaint comes back, scanning the code can pinpoint the process parameters and material batch from the production period. One lock factory relied on this practice to compress the investigation of a tooth break complaint from two weeks to one day. Customer perception of response speed often affects cooperation more than perception of the fault itself. Adding traceability codes to small parts costs almost nothing, but the return is at the level of trust.
Conclusion
Material selection judgment chain for small module gears:
First prioritize the character 'stable' (consistency in size and batch) → choose medium to low glass fiber abrasion-resistant system → then control drying and multi-cavity consistency.
If you have a small gear on hand for material determination, send over three things: torque transmission, required number of cycles, and assembly dimensional tolerances.
