Published at : 10 Jul 2024
Volume : IJtech
Vol 15, No 4 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i4.5675
Anas Ma’ruf | Faculty of Industrial Technology, Bandung Institute of Technology, Jl. Ganesha 10, Bandung, 40132, Indonesia |
Ali Akbar Ramadani Nasution | Faculty of Industrial Technology, Bandung Institute of Technology, Jl. Ganesha 10, Bandung, 40132, Indonesia |
Raden Achmad Chairdino Leuveano | Department of Industrial Engineering, Faculty of Industrial Engineering, Universitas Pembangunan Nasional “Veteran” Yogyakarta, Jl. Babarsari 2, Yogyakarta, 55281, Indonesia |
Estimating production costs is a challenging process for the Make-To-Order (MTO) industry because of
the product varieties, which leads to inaccurate cost estimation. The product
engineering process requires accurate assembly cost estimation to take
strategic decisions, specifically during the early design phase. Therefore, an
intelligent machine learning-based approach, namely Multi-linear Regression,
Random Forest, and Gradient Boosting, is proposed to estimate the assembly
design cost. This estimation is done by identifying the assembly features of
the 3D CAD model. The validation results showed that mate and assembly
features, as well as the number of parts, are effective cost drives, while
Random Forest outperformed other models. The proposed methodology is then
implemented in a cost estimation program and applied in the MTO industry. The proposed
estimation method deviated an average of 17.4% from the actual assembly design
cost, considered acceptable during the early design phase. In conclusion, the proposed
model and cost estimation program efficiently help the MTO industry predict
assembly design costs.
3D CAD; Assembly design; Assembly features; Cost estimation; Machine learning
Product
customization is increasingly implemented in the manufacturing industry to
improve competitiveness. Keil
(2024) found that
industries are motivated to meet new standards due to competitive pressures,
complex customer requirements, and stakeholder expectations. This phenomenon
has an impact, particularly on the production of the Make-to-Order (MTO)
industry (Yazdi,
Fini, and Forsythe, 2021). According to Yi et al. (2023), cost estimation
is the quantitative prediction of a product’s cost before completing all
product development stages. This implies that the MTO industry needs to
estimate product costs quickly and accurately. Unlike cost calculation, cost
estimation is based on the assumption that the industry lacks access to
manufacturing process data and with no conventional standard cost model (Latief,
Wibowo, and Isvara, 2013). Koonce
et al. (2003) and Bacharoudis
et al. (2021) stated that a systematic method is used for estimating
material and machining costs by classifying each material and production
operation into individual cost drivers.
Estimating assembly design cost is a more complex process, that includes intangible aspects, such as assembly parts and complexity (Castellani, Otri, and Pham, 2019; Demir et al., 2023). In the final design phase, the method used to estimate assembly design cost for mass production is significantly more developed. H’mida, Martin, and Vernadat (2006) and Niazi et al. (2006) have stated that this approach involves outlining the design activities cost, followed by identifying resources and operations during the design phase. Quintana and Ciurana (2011) have suggested that assembly design cost estimation is often performed by using a knowledge-based system, which is typically used in repetitive production.
With these points, this study proposes
systematic assembly design cost estimation as an alternative to the
conventional MTO approach. Conventional cost estimation is by constructing a
regression model based on complex relationships (Verlinden et al., 2008).
Also, the choice of
method is based on the limited access to manufacturing process data. Hence, the
estimation accuracy significantly affects industry profits. This implies that a
very low price reduces profits, while an extremely high price tends to affect
customer satisfaction negatively (Kalscheuer et al., 2023).
This study examines cost issues related to
initial assembly design in the MTO industry. It has been observed that the
industry produces a small volume of various assembly products, including
precision molding, stamping dies, precision spare parts, and mechanical
devices. The assembly design initiates the product’s engineering process based
on customer orders using specific 3D Computer-Aided Design (CAD) software. At
this phase, accurate cost estimation is essential for making strategic
decisions in the engineering process (Post et al., 2020). However, these detailed product features are typically not available
when using a conventional cost accounting approach. This caused Alfadhlani et al. (2019) to conclude that CAD data is needed when identifying feature
information based on assembly design, saved as historical data of industry
orders. To estimate
accurate assembly design costs, it is necessary to establish a relationship
between the product features and the historical assembly design cost. However,
using the conventional approach, it is challenging for cost engineers to
determine the product's sufficient cost function and behavior based on
experience (Bodendorf, Merkl, and Franke, 2021). Machine Learning (ML) method can be applied to solve
classification and prediction problems (Dawangi and Budiyanto, 2021; Alas and Ali, 2019;
Fagbola, Thakur, and Olugbara, 2019). ML method, as proposed by Durodola
(2022), Hammann (2024), and Ning et
al. (2020), is an efficient and accurate technique for identifying
the relationship between features and historical product cost. The model is
typically employed to overcome this problem as it detects hidden functional
relationships between assembly features and costs (Bodendorf, Merkl, and Franke, 2021). Other approaches to assembly cost estimation are analytical, knowledge-base,
or hybrid approaches (Mencaroni et al., 2023; Hagemann and Stark,
2020; Burggräf et al., 2019).
The main objectives of this study are (1) to
propose the ML method as a model for estimating assembly design costs based on
3D CAD data and (2) to create a program-based Graphical User Interface (GUI)
that engineers can use to quickly predict assembly design costs. In the MTO
industry, it is observed that customers always want to know the product price
ahead of time, and as a result, the preliminary price is expected to be close
to the final price.
Furthermore, to estimate target costs, actual product
cost data collected based on each 3D CAD file were used. The MTO company
specifically evaluated these models to ensure the cost values were consistent
with their estimates. Data
preprocessing was employed after data collection since it is
impossible to directly use the 3D CAD information as input for the ML method.
This step is crucial when analyzing the mate and assembly features, as well as
the number of parts that affect assembly design costs. Therefore, the
transformation of raw data into datasets began with developing a program to
extract the features in the 3D CAD file. After this extraction, data cleansing,
feature selection, and data transformation were performed.
Subsequently, an Application
Programming Interface (API) was utilized to read the 3D CAD file (Malpass, 2011). A command program was then
created using Python programming language, which generated a loop in data
reading, sequentially stored into data frames, known as the ML model’s input
dataset.
The ML method was chosen to
map the complex relationship between assembly design features and costs, based
on the input data, namely assembly features used to estimate the initial
assembly design costs. Therefore, this study proposes three ML methods, including
Multi-linear Regression, Random
Forest, and Gradient Boosting,
which each was developed and programmed with Python code.
Random Forest (RF) is a supervised ML algorithm that uses a tree-based ensemble learning to predict the output by combining various Decision Trees (DT) (Montesinos López et al., 2022; Rakhra et al., 2021). It is important to note that DTs exhibited distinct observations from the construction of a single DT. The RF algorithm representation using bootstrapping is shown in Figure 3. Bootstrapping uses distinct subsets of the available features to train multiple decision trees concurrently on different subsets of the training data set.
Furthermore, a random feature selection was
chosen based on the aggregation to train several decision trees in parallel (Misra and Li, 2020). Each tree was trained with a unique set of training data and features.
This is carried out to ensure that every decision tree is different from the
others, which can lower the variance of the RF model as a whole. The RF model
integrates the judgments made by each tree in order to achieve superior
generalization outcomes.
To
obtain a good estimation result, the RF model has hyperparameters that need to
be tuned, as shown in Table 1. These include 1)
Table 1 Hyperparameters search
space in GSCV
Parameter |
Range |
|
{10,50,100} |
Max features |
{‘auto’, ‘sqrt’, ‘log’} |
Max depth |
{5, 10, 18, None} |
Min sample split |
{2, 5, 10, 18, None} |
Min sample leaf |
{1, 5, 10, 18, None} |
Figure 4 The representation of the GB algorithm for
the case being studied. |
To expand the model's capability, the GB algorithm creates a number of regression trees over time. In a forward stepwise manner, the iteration of training process of the GB model to determine the proximate predicted value and the output is expressed in Equation (2) (Wang et al., 2020).
Table 2 Hyperparameter of the GB
model
Parameter |
Range |
|
{10,50,100} |
Learning rate |
{0.1, 0.3, 0.5, 1} |
Max depth |
{3, 5, 10, 20, None} |
The
assembly features, and the best model selected in the previous step served as a
reference when developing the application program of the proposed methodology.
Furthermore, the program aims to assist the industry in efficiently predicting
the assembly design cost based on the 3D CAD file.
A total of 104 historical datasets were collected on the
CAD assembly file, which includes the real assembly design of a MTO company.
Upon the completion of the dataset, the cost estimation model was developed,
trained, fine-tuned, and tested using the proposed methodology, as shown in
Figure 1. The three proposed models, namely MLR, RF, and GB, were employed to
estimate the product assembly design cost using training datasets. Table 3 shows the final experimental results of the proposed
model when tested with 20% datasets, while the results of training with 80% of
the datasets are omitted due to its brevity.
As observed in Table 3, the MLR algorithm has no hyperparameters, and hence no tuning was performed, and the and MAPE results obtained were 0.21 and 53%, respectively. Furthermore, only the five best combinations measured by and MAPE is shown in Table 3. The results showed that the RF-91 and the GB-43 models, with respective scores of 26.70% and 32.27% had the least significant MAPE values, while the RF-421 and GB-43 achieved the most significant score. Consequently, the GB-43 and RF-91 were selected as the best among their corresponding models, despite the RF scoring the highest and lowest MAPE. The optimum model was then determined by comparing the performance of MLR, RF-91, and GB-43 when predicting the best hyperparameter architecture.
Also, a re-experiment was conducted to fit
each model using all the training data. Every model’s cost was estimated with
the testing data to ensure that the best has the least significant MAPE value
and the most negligible difference in
Figure 5(a) depicts the program-based GUI where the user input a CAD assembly file. The program then uses the CAD's API to automatically identify the number of assembly features and the number of parts, as shown in Figure 5(b). Based on the proposed method, the user is subsequently presented with the estimated assembly design cost.
The results of the cost
estimation model and program development were discussed with the company
engineers, who discovered that two assembly design cases presented a
substantial predictive error value. Further analysis revealed that the product
assembly size was larger than in normal cases. In essence, when the product’s
size increases, the material volume required tends to be more, thereby causing
extra assembly design costs. This simply implies that the prediction model was limited in
estimating the design cost of homogeneous-sized product assembly. Based on
these findings, the proposed prediction model was accepted for use during the
early stage of assembly design.
This study examined the challenges
encountered when estimating the assembly design cost of the MTO industry. Cost
estimation entails early evaluation of various assembly parts, particularly
when information is limited. The proposed ML method for addressing the
challenge was found to be systematic, consistent, fast, and free of
subjectivity. The MLR, GB, and RF models are the ML method utilized to estimate
the assembly design cost. The experimental result showed that the RF model
exhibits the significant potential to efficiently estimate the assembly design
cost with an average deviation of 17.4% from the actual assembly design cost.
Therefore, the proposed model was developed into a practical application
program for MTO industries and considered viable for early assembly design cost
estimation where manufacturing information is incomplete. The model has been
integrated with CAD software to expedite and maintain consistency in assembly design
cost estimation. Nonetheless, the limitation of the proposed model relies on
the consistency of the historical dataset used for training the model. Future
research is directed to explore the impact of dynamic motions such as assembly
motion and kinematic behavior in assembly design cost estimation.
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