얇은 슬라이스에서 TTV 측정 방법: 9점 방법
추상적인: Total thickness variation (TTV) is the single number most often quoted for a
precision slicing process, and the easiest one to measure badly. This guide documents the nine-point grid
dual-probe method used in Ensoll’s slicing tests for
PEEK 그리고 PMI foam cut with a
다이아몬드 와이어 루프: how the sample is prepared, how it is held, where the nine points sit,
how TTV is calculated from them, and which errors produce a plausible but wrong number.
주요 요점
- TTV = Tmax – Tmin across a defined set of measurement points on one part; it is a within-part spread, not a flatness measurement.
- The standard pattern is a nine-point 3×3 grid – the smallest layout that samples centre, edges and diagonals, and fast enough to run on every sample in a batch.
- The sample must be cleaned, thermally stabilised and held on a vacuum chuck; a loose thin slice measures its own warpage as thickness.
- Always report TTV together with the nominal thickness: 0.036 mm on a 0.8 mm PMI foam slice and 0.085 mm on a 6.5 mm PEEK slice are not comparable raw numbers.
- Batch-level TTV trends are process signals; single-sample outliers are usually sample-handling problems.
What TTV Is – and What It Is Not
Total thickness variation is the spread of thickness across a single part. Measure the thickness at each
point of a defined grid, take the largest reading and the smallest reading, and subtract: the difference is the
TTV of that part. It says nothing about where the thick and thin areas are, and nothing about how the part
deviates from a plane – which is why it is normally reported alongside the flatness-family parameters rather
그들 대신에 ~보다.
| 매개변수 | 그것이 설명하는 것 | 참조 |
|---|---|---|
| TTV (total thickness variation) | 한 부분에서 가장 두꺼운 지점과 가장 얇은 지점 사이의 스프레드 | 부품 자체의 측정 격자 |
| 두께 편차 | 평균 두께가 명목치에서 얼마나 떨어져 있는지 | 명목치 (목표치) 두께 |
| 평탄도 | 표면이 기준 평면에서 벗어난 정도 | 이상적인 평면 |
| 활처럼 휨 / 뒤틀림 | 부품 전체의 곡률 | 이상적인 평면, 부품 전체에서 측정됨 |
| 테이퍼 | 한쪽 가장자리에서 다른 가장자리까지의 체계적인 두께 변화 | 서로 마주 보는 두 가장자리 |
TTV는 측정되는 두께와 동일한 단위로 표시됨. 정밀 슬라이싱 작업에서는 보통
마이크로미터 (um) 또는 밀리미터 (밀리미터), 그리고 명목 두께는 항상 함께 명시되어야 함 – TTV가
0.036 mm라는 것은 0.8 mm 슬라이스에서는 6.5 mm 슬라이스에서는 전혀 다른 의미.
TTV는 가공 기술보다는 측정 규율이지만, 프로세스가 제대로 작동할 때에만 그 가치를 발휘함
around it is under control. The wire selection, cooling strategy and kerf questions that sit upstream of the
number are covered in the 다이아몬드 와이어 루프 절단 기술 FAQ, and the range of
workpiece materials the method is applied to is summarised in the guide to
다이아몬드 와이어 루프 절단에 적합한 재료.
Equipment Needed
- A thickness measuring instrument with two opposed probes, so the reading is the true part thickness rather
than a distance to a reference surface. - A vacuum chuck stage that holds the sample flat by negative pressure.
- A standard thickness block for calibration.
- A thermal stabilisation period – the instrument, the sample and the room should be at the same temperature
before measurement, to remove zero drift and systematic error. - A dust-free preparation area, so that particles on the sample surface do not enter the readings.
The Nine-Point Procedure
- Thermally stabilise and calibrate. Warm the instrument up at constant temperature and
calibrate it with the standard thickness block, to reduce zero drift and systematic error. - Clean the sample. Remove dust and loose debris from both faces. On a sliced foam or
composite, debris at the surface is a thickness error, not a cleanliness issue. - Mount on the vacuum chuck. Centre the sample and hold it by negative pressure. This keeps
the sample in a stable measuring state and limits the effect of position shift, local warping and deformation
on the readings. - Define the grid. Mark nine positions in a 3×3 pattern – three rows of three, spanning the
centre and the edge regions of the part. The same grid must be used for every sample in the batch. - Collect readings in sequence. Measure the nine positions in the same order on every
sample, so that any instrument drift is distributed identically instead of landing on one sample. - Take Tmax and Tmin and subtract. TTV = Tmax – Tmin for that sample. The result describes
that one part; batch consistency is judged by comparing TTV across samples.
Worked Example
From the PMI foam slicing test, sample S01 gave nine readings of 0.785, 0.790, 0.799 / 0.800, 0.802, 0.812
/ 0.819, 0.832, 0.835 밀리미터. Tmax is 0.835 mm and Tmin is 0.785 밀리미터, so:
TTV = 0.835 – 0.785 = 0.050 밀리미터
The same sample measured for dimensional tolerance averaged 0.808 mm against a 0.800 mm nominal thickness,
a deviation of +0.008 밀리미터. Those two numbers answer different questions: the deviation says the slice is near
the target thickness, while the TTV says how much it varies across its own area. A process can hold thickness
well and still have poor TTV.
Reference TTV Values from Diamond Wire Cutting
| 재료 | Slice produced | TTV | 두께 허용 | Ra | Max chipping |
|---|---|---|---|---|---|
| PMI foam | 400 x 400 x 0.8 밀리미터 | 0.013-0.050 밀리미터, mean 0.036 밀리미터 | +/-0.043 밀리미터 | 0.68-0.82 um | 7.1 um |
| PEEK | 6.5 x 60 x 60 밀리미터 | 0.072-0.098 밀리미터, mean 0.085 밀리미터 | +/-0.037 밀리미터 | 0.76-0.95 um | 6.7 um |
Three Ways to Get a Wrong Number
Measuring a sample that is not held flat
A thin slice laid loose on a surface measures its own warpage as well as its thickness. The vacuum chuck
exists to remove that variable; skipping it typically inflates TTV on thin parts rather than reducing it.
Comparing TTV across nominal thicknesses
A raw TTV value is only meaningful against the nominal thickness and the application tolerance. The PMI
foam figure of 0.036 mm average sounds tighter than the PEEK figure of 0.085 mm average, but the slices were
0.8 mm and 6.5 mm thick respectively. Report the nominal thickness with every TTV value or the comparison is
misleading.
Reading TTV as a flatness measurement
TTV does not tell you whether the part is bowed or warped, and a low TTV does not guarantee a flat part.
Where flatness matters, measure it separately, on the same sample, 적절한 기준면을 사용하면
메서드.
공정 제어에서 TTV 사용
9점 방법은 빠르고 반복 가능하기 때문, 실제 값은 비교 가능하다: 모든 샘플에 대해 실행
배치로 진행 및 결과 패턴이 공정의 안정성을 알려준다. TTV가 높은 단일 샘플
그 샘플을 가리킴; 공정을 기준으로 상승하는 배치 – 대부분 와이어 상태, 장력
안정성 또는 고정구 지지. PMI 폼 테스트에서 네 샘플이 TTV를 얻었으며 0.050, 0.037, 0.044 그리고
0.013 밀리미터, 마지막 샘플에서 가장 작은 값, 슬라이스 두께 일관성을 나타내며
샘플 간 산란이 체계적인 추세가 아니다.
자주 묻는 질문
정밀 절단에서 TTV는 무엇을 의미하는가?
TTV는 전체 두께 변동을 의미한다. 한 부품의 정의된 측정점 집합에서 가장 두꺼운 값과 가장 얇은 값의 차이. 슬라이스 웨이퍼에서, 플레이트나 폼 시트에서 절단의 균일성을 나타내는 주요 지표, 두께와 동일한 단위로 표현되며 – 마이크로미터 또는 밀리미터.
TTV는 평탄도와 어떻게 다른가, 보우와 휘름?
TTV는 한 부품의 두께 값 분포를 설명한다. 평탄도, 보우와 휘기는 부품이 기준면에서 벗어나는 방식을 설명한다 – 부품이 균일하게 얇아도 여전히 휘어질 수 있다. 슬라이싱 공정은 좋은 TTV를 보일 수 있으면서도 평평함이 나쁘다는 뜻, 그래서 두 가지를 별도로 보고하는 이유.
왜 더 많거나 적은 점 대신 9점을 사용하는가?
9점 3×3 그리드는 중심을 샘플링하는 가장 작은 패턴, the edges and the diagonal directions, so it can detect a thickness gradient across the slice rather than only a random scatter. It is also quick enough to run on every sample in a batch, which makes results comparable across samples and across materials.
Why must the sample be held on a vacuum chuck?
A thin slice is flexible. If it is simply laid on a surface, its own weight and any local warping change the reading. Holding it by negative pressure on a vacuum chuck keeps it in a repeatable measuring state and limits the effect of position shift, local warping and deformation on the thickness readings.
What TTV values has diamond wire cutting achieved?
On 0.8 mm PMI foam slices, TTV ranged from 0.013 받는 사람 0.050 mm with an average of 0.036 밀리미터. On 6.5 mm PEEK slices, TTV ranged from 0.072 받는 사람 0.098 mm with an average of 0.085 밀리미터. Because the parts differ in nominal thickness and material, compare each against its own application tolerance.
Ensoll 엔지니어링 팀이 검토한 기술 내용 – 다이아몬드 와이어 루프 제조사와 함께 10+ 다년간의 생산 경험을 가진 회사.
