# A Review of the High-Mix, Low-Volume Manufacturing Industry
## 3 Current Status of HMLV Research
### Number of Publications over the Two Decades
#### 3.1.1 Publication Keywords Co-Occurrence  
2000-2008 Phase  
The keywords are grouped into two clusters in the earliest time segment of the literature search in Figure 4. The red cluster denotes work related to printed circuit board assembly (PCBA), while the green cluster relates to manufacturing simulation. The research keywords showed a considerable emphasis on the research on manufacturing printed circuit boards. Algorithms and simulations work was for optimisation in the production and operation management challenges, such as scheduling and levelling.  
2009-2016 Phase  
From 2009 to 2016, Figure 5 shows that new research topics emerged as there was more interest in automation and robotics in manufacturing industries, as the concept of Industry 4.0 could bring more flexibility for HMLV manufacturing.  
Figure 4: Publication keywords co-occurrence cluster during the 2000–2008 Phase.  
Figure 5: Publication keywords co-occurrence according to topics’ average publication year (2009–2016 phase).  
Earlier research, in the 2010s, mainly focused on algorithms, such as genetic algorithms, to solve production and operation management problems. However, after 2013, the implementation of HMLV in the automated production system became the focus. For example, the topic of production control involving automation and robotics was popular. Maintenance and product design were the two new important aspects of the research in an HMLV environment.  
The research focuses also moved from PCBA to the challenges of the broader semiconductor industry. The HMLV job shop nature of the industry requires production planning and control. Two main topics were frequently discussed--maintenance and automation.  
2017-2022 Phase  
Figure 6 shows the topics of interest from 2017 to October 2022 with five main clusters. Yellow clusters are mainly on robotics and automation. Manual assembly and lean topics are shown in red. The dark blue cluster focuses mostly on production planning and control methods, such as order release and workload control with simulations. At the same time, light blue shows the manufacturing consideration of production resource management, such as scheduling, costs, decision making, and assembly machines. The green cluster shows Industry 4.0-related topics and the semiconductor industry. Meanwhile, purple relates operation research and management science with algorithms and optimisation.  
The development in 2017-2022 in Figure 7, saw a growing interest in research in the popular topics of Industry 4.0--robotics, artificial intelligence, the internet of things, and additive manufacturing.  
Figure 6: Publication keyword co-occurrence cluster during the 2017–October 2022 phase.  
Research for industrial robotics and automation for flexible manufacturing were made to make robotic programming easier and more flexible. Techniques, such as deep learning, is a popular keyword in these studies. The concept of Industry 4.0 also hoped to improve the productivity of manual and semi-automated manufacturing. Therefore, human-robot collaboration was an area of interest to cater for the flexible HMLV manufacturing environment.  
Instead of algorithms, the researchers looked at a broader ecosystem of production planning. Collecting production data in real-time to build big data, enables a more comprehensive data analysis for decision-making systems. Together with forecasting and reinforced learning, these were the three keywords that came up after 2020.